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Why `cp` is designed this way to overwrite existing files silently?
Clash Royale CLAN TAG#URR8PPP
up vote
1
down vote
favorite
I create such commands to test cp commands
In [98]: ls
first.html second.html third.html
In [99]: less first.html second.html third.html
In [100]: cat first.html
first
In [101]: cat second.html
second
In [102]: cat third.html
third
When I copy first.html to second.html,
In [103]: cp first.html second.html
In [104]: cat second.html
first
The second.html is overwritten silently without any error prompts.
Nonetheless, If I do it in the desktop GUI, draw a file in with the same name, it will be suffixed an first1.html automatically.
Doing this avoided to overwrite an existing file accidentally.
Why not follow this pattern to design cp but to overwrite silently.
I am learning python now and found that it's shutil.copy completely inherit from the idea of command cp.
I assume it not a good design and could be easily amended by insert an if check.
Why cp is designed this way to overwrite existing files silently?
cp history
edited 2 hours ago
dhag
10.9k32842
asked 3 hours ago
rider dragon
1083
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up vote
1
down vote
favorite
I create such commands to test cp commands
In [98]: ls
first.html second.html third.html
In [99]: less first.html second.html third.html
In [100]: cat first.html
first
In [101]: cat second.html
second
In [102]: cat third.html
third
When I copy first.html to second.html,
In [103]: cp first.html second.html
In [104]: cat second.html
first
The second.html is overwritten silently without any error prompts.
Nonetheless, If I do it in the desktop GUI, draw a file in with the same name, it will be suffixed an first1.html automatically.
Doing this avoided to overwrite an existing file accidentally.
Why not follow this pattern to design cp but to overwrite silently.
I am learning python now and found that it's shutil.copy completely inherit from the idea of command cp.
I assume it not a good design and could be easily amended by insert an if check.
Why cp is designed this way to overwrite existing files silently?
cp history
edited 2 hours ago
dhag
10.9k32842
asked 3 hours ago
rider dragon
1083
New contributor
rider dragon is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
3
I imagine only the coreutils designers can truly answer the question, but it's just the way it works for now. Usually the apps are built assuming the user really means what they're doing and to minimize the extra prompting. If you want to change the behavior, alias 'cp' to 'cp -i' or 'cp -n'.
– kevlinux
2 hours ago
Is it "do one thing at one time"? @kevlinux
– rider dragon
1 hour ago
add a comment |Â
up vote
1
down vote
favorite
up vote
1
down vote
favorite
I create such commands to test cp commands
In [98]: ls
first.html second.html third.html
In [99]: less first.html second.html third.html
In [100]: cat first.html
first
In [101]: cat second.html
second
In [102]: cat third.html
third
When I copy first.html to second.html,
In [103]: cp first.html second.html
In [104]: cat second.html
first
The second.html is overwritten silently without any error prompts.
Nonetheless, If I do it in the desktop GUI, draw a file in with the same name, it will be suffixed an first1.html automatically.
Doing this avoided to overwrite an existing file accidentally.
Why not follow this pattern to design cp but to overwrite silently.
I am learning python now and found that it's shutil.copy completely inherit from the idea of command cp.
I assume it not a good design and could be easily amended by insert an if check.
Why cp is designed this way to overwrite existing files silently?
cp history
edited 2 hours ago
dhag
10.9k32842
asked 3 hours ago
rider dragon
1083
New contributor
rider dragon is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
I create such commands to test cp commands
In [98]: ls
first.html second.html third.html
In [99]: less first.html second.html third.html
In [100]: cat first.html
first
In [101]: cat second.html
second
In [102]: cat third.html
third
When I copy first.html to second.html,
In [103]: cp first.html second.html
In [104]: cat second.html
first
The second.html is overwritten silently without any error prompts.
Nonetheless, If I do it in the desktop GUI, draw a file in with the same name, it will be suffixed an first1.html automatically.
Doing this avoided to overwrite an existing file accidentally.
Why not follow this pattern to design cp but to overwrite silently.
I am learning python now and found that it's shutil.copy completely inherit from the idea of command cp.
I assume it not a good design and could be easily amended by insert an if check.
Why cp is designed this way to overwrite existing files silently?
cp history
cp history
edited 2 hours ago
dhag
10.9k32842
asked 3 hours ago
rider dragon
1083
New contributor
rider dragon is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 2 hours ago
dhag
10.9k32842
asked 3 hours ago
rider dragon
1083
New contributor
rider dragon is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 2 hours ago
dhag
10.9k32842
edited 2 hours ago
dhag
10.9k32842
edited 2 hours ago
dhag
10.9k32842
10.9k32842
asked 3 hours ago
rider dragon
1083
New contributor
rider dragon is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 3 hours ago
rider dragon
1083
asked 3 hours ago
rider dragon
1083
1083
New contributor
rider dragon is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
rider dragon is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
rider dragon is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
3
I imagine only the coreutils designers can truly answer the question, but it's just the way it works for now. Usually the apps are built assuming the user really means what they're doing and to minimize the extra prompting. If you want to change the behavior, alias 'cp' to 'cp -i' or 'cp -n'.
– kevlinux
2 hours ago
Is it "do one thing at one time"? @kevlinux
– rider dragon
1 hour ago
add a comment |Â
3
I imagine only the coreutils designers can truly answer the question, but it's just the way it works for now. Usually the apps are built assuming the user really means what they're doing and to minimize the extra prompting. If you want to change the behavior, alias 'cp' to 'cp -i' or 'cp -n'.
– kevlinux
2 hours ago
Is it "do one thing at one time"? @kevlinux
– rider dragon
1 hour ago
3
3
I imagine only the coreutils designers can truly answer the question, but it's just the way it works for now. Usually the apps are built assuming the user really means what they're doing and to minimize the extra prompting. If you want to change the behavior, alias 'cp' to 'cp -i' or 'cp -n'.
– kevlinux
2 hours ago
I imagine only the coreutils designers can truly answer the question, but it's just the way it works for now. Usually the apps are built assuming the user really means what they're doing and to minimize the extra prompting. If you want to change the behavior, alias 'cp' to 'cp -i' or 'cp -n'.
– kevlinux
2 hours ago
Is it "do one thing at one time"? @kevlinux
– rider dragon
1 hour ago
Is it "do one thing at one time"? @kevlinux
– rider dragon
1 hour ago
add a comment |Â
2 Answers
2
active
oldest
votes
up vote
3
down vote
accepted
The default overwrite behavior of cp is specified in POSIX.
If source_file is of type regular file, the following steps shall be taken:
3.a. The behavior is unspecified if dest_file exists and was written by a previous step. Otherwise, if dest_file exists, the following steps shall be taken:
3.a.i. If the -i option is in effect, the cp utility shall write a prompt to the standard error and read a line from the standard input. If the response is not affirmative, cp shall do nothing more with source_file and go on to any remaining files.
3.a.ii. A file descriptor for dest_file shall be obtained by performing actions equivalent to the open() function defined in the System Interfaces volume of POSIX.1-2017 called using dest_file as the path argument, and the bitwise-inclusive OR of O_WRONLY and O_TRUNC as the oflag argument.
3.a.iii. If the attempt to obtain a file descriptor fails and the -f option is in effect, cp shall attempt to remove the file by performing actions equivalent to the unlink() function defined in the System Interfaces volume of POSIX.1-2017 called using dest_file as the path argument. If this attempt succeeds, cp shall continue with step 3b.
When the POSIX specification was written, there already was a large number of scripts in existence, with a built-in assumption for the default overwrite behavior. Many of those scripts were designed to run without direct user presence, e.g. as cron jobs or other background tasks. Changing the behavior would have broken them. Reviewing and modifying them all to add an option to force overwriting wherever needed was probably considered a huge task with minimal benefits.
Also, the Unix command line was always designed to allow an experienced user to work efficiently, even at the expense of a hard learning curve for a beginner. When the user enters a command, the computer is to expect that the user really means it, without any second-guessing; it is the user's responsibility to be careful with potentially destructive commands.
answered 1 hour ago
telcoM
13.1k11440
add a comment |Â
up vote
2
down vote
You may insert the "if check" yourself with
alias cp='cp -i'
The -i option to cp makes it ask interactively if the operation would overwrite the target and with the above alias, your interactive use of cp would enable this option by default.
The cp utility is often used in scripts. These scripts may not always be run manually, but may be part of system maintenance tasks run by via cron or some similar facility. In those cases, there are no humans to ask for confirmation.
To have a script avoid overwriting a file with cp one may insert an explicit check:
if [ -e "$target" ]; then
printf '%s already exists, refusing to overwriten' "$target" >&2
exit 1
fi
cp "$source" "$target"
I'm opting for exiting the script with an error message if $target exists in the above example. The existence of the target is obviously unexpected, and allowing the script to continue after detecting this may lead to other more severe issues.
answered 13 mins ago
Kusalananda
111k15216342
add a comment |Â
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
3
down vote
accepted
The default overwrite behavior of cp is specified in POSIX.
If source_file is of type regular file, the following steps shall be taken:
3.a. The behavior is unspecified if dest_file exists and was written by a previous step. Otherwise, if dest_file exists, the following steps shall be taken:
3.a.i. If the -i option is in effect, the cp utility shall write a prompt to the standard error and read a line from the standard input. If the response is not affirmative, cp shall do nothing more with source_file and go on to any remaining files.
3.a.ii. A file descriptor for dest_file shall be obtained by performing actions equivalent to the open() function defined in the System Interfaces volume of POSIX.1-2017 called using dest_file as the path argument, and the bitwise-inclusive OR of O_WRONLY and O_TRUNC as the oflag argument.
3.a.iii. If the attempt to obtain a file descriptor fails and the -f option is in effect, cp shall attempt to remove the file by performing actions equivalent to the unlink() function defined in the System Interfaces volume of POSIX.1-2017 called using dest_file as the path argument. If this attempt succeeds, cp shall continue with step 3b.
When the POSIX specification was written, there already was a large number of scripts in existence, with a built-in assumption for the default overwrite behavior. Many of those scripts were designed to run without direct user presence, e.g. as cron jobs or other background tasks. Changing the behavior would have broken them. Reviewing and modifying them all to add an option to force overwriting wherever needed was probably considered a huge task with minimal benefits.
Also, the Unix command line was always designed to allow an experienced user to work efficiently, even at the expense of a hard learning curve for a beginner. When the user enters a command, the computer is to expect that the user really means it, without any second-guessing; it is the user's responsibility to be careful with potentially destructive commands.
answered 1 hour ago
telcoM
13.1k11440
add a comment |Â
up vote
3
down vote
accepted
The default overwrite behavior of cp is specified in POSIX.
If source_file is of type regular file, the following steps shall be taken:
3.a. The behavior is unspecified if dest_file exists and was written by a previous step. Otherwise, if dest_file exists, the following steps shall be taken:
3.a.i. If the -i option is in effect, the cp utility shall write a prompt to the standard error and read a line from the standard input. If the response is not affirmative, cp shall do nothing more with source_file and go on to any remaining files.
3.a.ii. A file descriptor for dest_file shall be obtained by performing actions equivalent to the open() function defined in the System Interfaces volume of POSIX.1-2017 called using dest_file as the path argument, and the bitwise-inclusive OR of O_WRONLY and O_TRUNC as the oflag argument.
3.a.iii. If the attempt to obtain a file descriptor fails and the -f option is in effect, cp shall attempt to remove the file by performing actions equivalent to the unlink() function defined in the System Interfaces volume of POSIX.1-2017 called using dest_file as the path argument. If this attempt succeeds, cp shall continue with step 3b.
When the POSIX specification was written, there already was a large number of scripts in existence, with a built-in assumption for the default overwrite behavior. Many of those scripts were designed to run without direct user presence, e.g. as cron jobs or other background tasks. Changing the behavior would have broken them. Reviewing and modifying them all to add an option to force overwriting wherever needed was probably considered a huge task with minimal benefits.
Also, the Unix command line was always designed to allow an experienced user to work efficiently, even at the expense of a hard learning curve for a beginner. When the user enters a command, the computer is to expect that the user really means it, without any second-guessing; it is the user's responsibility to be careful with potentially destructive commands.
answered 1 hour ago
telcoM
13.1k11440
add a comment |Â
up vote
3
down vote
accepted
up vote
3
down vote
accepted
The default overwrite behavior of cp is specified in POSIX.
If source_file is of type regular file, the following steps shall be taken:
3.a. The behavior is unspecified if dest_file exists and was written by a previous step. Otherwise, if dest_file exists, the following steps shall be taken:
3.a.i. If the -i option is in effect, the cp utility shall write a prompt to the standard error and read a line from the standard input. If the response is not affirmative, cp shall do nothing more with source_file and go on to any remaining files.
3.a.ii. A file descriptor for dest_file shall be obtained by performing actions equivalent to the open() function defined in the System Interfaces volume of POSIX.1-2017 called using dest_file as the path argument, and the bitwise-inclusive OR of O_WRONLY and O_TRUNC as the oflag argument.
3.a.iii. If the attempt to obtain a file descriptor fails and the -f option is in effect, cp shall attempt to remove the file by performing actions equivalent to the unlink() function defined in the System Interfaces volume of POSIX.1-2017 called using dest_file as the path argument. If this attempt succeeds, cp shall continue with step 3b.
When the POSIX specification was written, there already was a large number of scripts in existence, with a built-in assumption for the default overwrite behavior. Many of those scripts were designed to run without direct user presence, e.g. as cron jobs or other background tasks. Changing the behavior would have broken them. Reviewing and modifying them all to add an option to force overwriting wherever needed was probably considered a huge task with minimal benefits.
Also, the Unix command line was always designed to allow an experienced user to work efficiently, even at the expense of a hard learning curve for a beginner. When the user enters a command, the computer is to expect that the user really means it, without any second-guessing; it is the user's responsibility to be careful with potentially destructive commands.
answered 1 hour ago
telcoM
13.1k11440
The default overwrite behavior of cp is specified in POSIX.
If source_file is of type regular file, the following steps shall be taken:
3.a. The behavior is unspecified if dest_file exists and was written by a previous step. Otherwise, if dest_file exists, the following steps shall be taken:
3.a.i. If the -i option is in effect, the cp utility shall write a prompt to the standard error and read a line from the standard input. If the response is not affirmative, cp shall do nothing more with source_file and go on to any remaining files.
3.a.ii. A file descriptor for dest_file shall be obtained by performing actions equivalent to the open() function defined in the System Interfaces volume of POSIX.1-2017 called using dest_file as the path argument, and the bitwise-inclusive OR of O_WRONLY and O_TRUNC as the oflag argument.
3.a.iii. If the attempt to obtain a file descriptor fails and the -f option is in effect, cp shall attempt to remove the file by performing actions equivalent to the unlink() function defined in the System Interfaces volume of POSIX.1-2017 called using dest_file as the path argument. If this attempt succeeds, cp shall continue with step 3b.
When the POSIX specification was written, there already was a large number of scripts in existence, with a built-in assumption for the default overwrite behavior. Many of those scripts were designed to run without direct user presence, e.g. as cron jobs or other background tasks. Changing the behavior would have broken them. Reviewing and modifying them all to add an option to force overwriting wherever needed was probably considered a huge task with minimal benefits.
Also, the Unix command line was always designed to allow an experienced user to work efficiently, even at the expense of a hard learning curve for a beginner. When the user enters a command, the computer is to expect that the user really means it, without any second-guessing; it is the user's responsibility to be careful with potentially destructive commands.
answered 1 hour ago
telcoM
13.1k11440
answered 1 hour ago
telcoM
13.1k11440
answered 1 hour ago
telcoM
13.1k11440
answered 1 hour ago
telcoM
13.1k11440
13.1k11440
add a comment |Â
add a comment |Â
up vote
2
down vote
You may insert the "if check" yourself with
alias cp='cp -i'
The -i option to cp makes it ask interactively if the operation would overwrite the target and with the above alias, your interactive use of cp would enable this option by default.
The cp utility is often used in scripts. These scripts may not always be run manually, but may be part of system maintenance tasks run by via cron or some similar facility. In those cases, there are no humans to ask for confirmation.
To have a script avoid overwriting a file with cp one may insert an explicit check:
if [ -e "$target" ]; then
printf '%s already exists, refusing to overwriten' "$target" >&2
exit 1
fi
cp "$source" "$target"
I'm opting for exiting the script with an error message if $target exists in the above example. The existence of the target is obviously unexpected, and allowing the script to continue after detecting this may lead to other more severe issues.
answered 13 mins ago
Kusalananda
111k15216342
add a comment |Â
up vote
2
down vote
You may insert the "if check" yourself with
alias cp='cp -i'
The -i option to cp makes it ask interactively if the operation would overwrite the target and with the above alias, your interactive use of cp would enable this option by default.
The cp utility is often used in scripts. These scripts may not always be run manually, but may be part of system maintenance tasks run by via cron or some similar facility. In those cases, there are no humans to ask for confirmation.
To have a script avoid overwriting a file with cp one may insert an explicit check:
if [ -e "$target" ]; then
printf '%s already exists, refusing to overwriten' "$target" >&2
exit 1
fi
cp "$source" "$target"
I'm opting for exiting the script with an error message if $target exists in the above example. The existence of the target is obviously unexpected, and allowing the script to continue after detecting this may lead to other more severe issues.
answered 13 mins ago
Kusalananda
111k15216342
add a comment |Â
up vote
2
down vote
up vote
2
down vote
You may insert the "if check" yourself with
alias cp='cp -i'
The -i option to cp makes it ask interactively if the operation would overwrite the target and with the above alias, your interactive use of cp would enable this option by default.
The cp utility is often used in scripts. These scripts may not always be run manually, but may be part of system maintenance tasks run by via cron or some similar facility. In those cases, there are no humans to ask for confirmation.
To have a script avoid overwriting a file with cp one may insert an explicit check:
if [ -e "$target" ]; then
printf '%s already exists, refusing to overwriten' "$target" >&2
exit 1
fi
cp "$source" "$target"
I'm opting for exiting the script with an error message if $target exists in the above example. The existence of the target is obviously unexpected, and allowing the script to continue after detecting this may lead to other more severe issues.
answered 13 mins ago
Kusalananda
111k15216342
You may insert the "if check" yourself with
alias cp='cp -i'
The -i option to cp makes it ask interactively if the operation would overwrite the target and with the above alias, your interactive use of cp would enable this option by default.
The cp utility is often used in scripts. These scripts may not always be run manually, but may be part of system maintenance tasks run by via cron or some similar facility. In those cases, there are no humans to ask for confirmation.
To have a script avoid overwriting a file with cp one may insert an explicit check:
if [ -e "$target" ]; then
printf '%s already exists, refusing to overwriten' "$target" >&2
exit 1
fi
cp "$source" "$target"
I'm opting for exiting the script with an error message if $target exists in the above example. The existence of the target is obviously unexpected, and allowing the script to continue after detecting this may lead to other more severe issues.
answered 13 mins ago
Kusalananda
111k15216342
edited 4 mins ago
answered 13 mins ago
Kusalananda
111k15216342
answered 13 mins ago
Kusalananda
111k15216342
answered 13 mins ago
Kusalananda
111k15216342
111k15216342
add a comment |Â
add a comment |Â
rider dragon is a new contributor. Be nice, and check out our Code of Conduct.
rider dragon is a new contributor. Be nice, and check out our Code of Conduct.
rider dragon is a new contributor. Be nice, and check out our Code of Conduct.
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3
I imagine only the coreutils designers can truly answer the question, but it's just the way it works for now. Usually the apps are built assuming the user really means what they're doing and to minimize the extra prompting. If you want to change the behavior, alias 'cp' to 'cp -i' or 'cp -n'.
– kevlinux
2 hours ago
Is it "do one thing at one time"? @kevlinux
– rider dragon
1 hour ago