What does cut return if the specified field does not exist?

up vote
3
down vote

favorite

I have a string:

6.40.4

and a second one:

6.40

I am using var=$(echo $versionfull | cut -d'.' -f3) to get the third digit from the first string in bash. What does this command return for the second one? It looks empty but either [ -z $var ] or [ $var == "" ] does not work. I want to give it a value of 0 in case of a second string.

edited Aug 29 at 20:21

Jeff Schaller

32.1k849109

asked Aug 29 at 19:17

Kliwer

182

2

Pipe it to od to see what it returns...
â€“Â don_crissti
Aug 29 at 19:28

add a commentÂ |Â

up vote
3
down vote

favorite

I have a string:

6.40.4

and a second one:

6.40

edited Aug 29 at 20:21

Jeff Schaller

32.1k849109

asked Aug 29 at 19:17

Kliwer

182

2

Pipe it to od to see what it returns...
â€“Â don_crissti
Aug 29 at 19:28

add a commentÂ |Â

up vote
3
down vote

favorite

I have a string:

6.40.4

and a second one:

6.40

edited Aug 29 at 20:21

Jeff Schaller

32.1k849109

asked Aug 29 at 19:17

Kliwer

182

I have a string:

6.40.4

and a second one:

6.40

edited Aug 29 at 20:21

Jeff Schaller

32.1k849109

asked Aug 29 at 19:17

Kliwer

182

edited Aug 29 at 20:21

Jeff Schaller

32.1k849109

edited Aug 29 at 20:21

Jeff Schaller

32.1k849109

edited Aug 29 at 20:21

Jeff Schaller

32.1k849109

asked Aug 29 at 19:17

Kliwer

182

asked Aug 29 at 19:17

Kliwer

182

asked Aug 29 at 19:17

Kliwer

182

2

Pipe it to od to see what it returns...
â€“Â don_crissti
Aug 29 at 19:28

add a commentÂ |Â

2

Pipe it to od to see what it returns...
â€“Â don_crissti
Aug 29 at 19:28

Pipe it to od to see what it returns...
â€“Â don_crissti
Aug 29 at 19:28

add a commentÂ |Â

4 Answers
4

active

oldest

votes

up vote
8
down vote

accepted

You could use var=$(echo "$versionfull.0" | cut -d'.' -f3).

In the first case, versionfull will contain 6.40.4.0, ignoring the padding and returning 4 as needed. In the second case, the .0 will be padded and returned.

edited Aug 29 at 20:09

StÃ©phane Chazelas

283k53521856

answered Aug 29 at 19:26

ThoriumBR

1984

Thanks. This is simple and works exactly like I want it to.
â€“Â Kliwer
Aug 29 at 19:39

3

It's sad that this is marked as the solution because it doesn't even answer the question, which is what everyone will expect to find when they come here in the future with the same question. Maybe the question should be changed to reflect that OP doesn't actually care about what it returns.
â€“Â pipe
Aug 30 at 9:28

You are right, it does not answers the question, but it solves OP problem. Is tailored for this only case, but that's all OP wants - solve his problem.
â€“Â ThoriumBR
Aug 30 at 11:43

add a commentÂ |Â

up vote
10
down vote

To answer your direct question, cut returns nothing except a trailing newline, as per the spec (thanks to don_crissti for that reference):

echo "$versionfull" | cut -d. -f3 | od -c
0000000 n
0000001

If you have a shell that supports here-strings, you could do the following:

IFS=. read a b c <<< "$versionfull"

Notice the quoting for $versionfull, in case it ever had whitespace (anything from $IFS).

If you think that c might be empty, then ask to set it to zero:

c=$c:-0

edited Aug 29 at 19:49

answered Aug 29 at 19:27

Jeff Schaller

32.1k849109

2

Note that the need to quote in IFS=. read a b c <<< "$versionfull" was only for older versions of bash; other shells and newer versions of bash don't have the problem.
â€“Â StÃ©phane Chazelas
Aug 29 at 19:43

Note that if the input has only one field, cut returns that field.
â€“Â StÃ©phane Chazelas
Aug 29 at 20:05

add a commentÂ |Â

up vote
6
down vote

cut has an odd API.

cut -f n will output the n^th field of each line that has at least one delimiter (empty if the line has fewer than n-1 delimiters (fewer than n fields)), and returns the full line (so the first field) for those that don't have any delimiter:

$ echo a.b.c | cut -d. -f3
c
$ echo a.b | cut -d. -f3

$ echo a | cut -d. -f3
a

So the answer to What does cut return if the specified field does not exist? is either the first field or an empty field depending on whether the input line has one field or more.

You can add the -s option to remove the lines that don't have any delimiter to avoid that weird last case above, but that's generally not what you want (you'd generally want to consider that input line to have an empty 3^rd field instead of skipping it altogether), and that's worth if you want the first field:

$ echo a | cut -sd. -f2
$ echo a | cut -sd. -f1
$

(you asked for the first field, the input has only one field, but you don't get any output because the input has no delimiter).

So @ThoriumBR's suggestion to add a .0 is a very good one. Without it:

versionfull=5
echo "$versionfull" | cut -d. -f3

would actually output 5. By adding .0, we make sure the input has at least one delimiter. I would go further and use:

echo "$versionfull.0.0" | cut -d. -f3

To make sure the input has at least 3 fields.

edited Aug 30 at 6:40

answered Aug 29 at 20:02

StÃ©phane Chazelas

283k53521856

The probability of version 7 in Mikrotik is low ;) Anyway, thanks - I'll do that.
â€“Â Kliwer
Aug 29 at 20:11

How does this relate to his second case? The input has a delimiter.
â€“Â Barmar
Aug 29 at 22:59

add a commentÂ |Â

up vote
1
down vote

It sets it to an empty string. You should quote the variable when using it with the [ command.

if [ "$var" == "" ]
then echo "Var is empty"
fi

Without the quotes, the first line expands to:

if [ == "" ]

which is invalid syntax because == requires a parameter to the left of it.

answered Aug 29 at 23:03

Barmar

6,7201122

add a commentÂ |Â

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4 Answers
4

active

oldest

votes

4 Answers
4

active

oldest

votes

up vote
8
down vote

accepted

You could use var=$(echo "$versionfull.0" | cut -d'.' -f3).

In the first case, versionfull will contain 6.40.4.0, ignoring the padding and returning 4 as needed. In the second case, the .0 will be padded and returned.

edited Aug 29 at 20:09

StÃ©phane Chazelas

283k53521856

answered Aug 29 at 19:26

ThoriumBR

1984

Thanks. This is simple and works exactly like I want it to.
â€“Â Kliwer
Aug 29 at 19:39

3

It's sad that this is marked as the solution because it doesn't even answer the question, which is what everyone will expect to find when they come here in the future with the same question. Maybe the question should be changed to reflect that OP doesn't actually care about what it returns.
â€“Â pipe
Aug 30 at 9:28

You are right, it does not answers the question, but it solves OP problem. Is tailored for this only case, but that's all OP wants - solve his problem.
â€“Â ThoriumBR
Aug 30 at 11:43

add a commentÂ |Â

up vote
8
down vote

accepted

You could use var=$(echo "$versionfull.0" | cut -d'.' -f3).

In the first case, versionfull will contain 6.40.4.0, ignoring the padding and returning 4 as needed. In the second case, the .0 will be padded and returned.

edited Aug 29 at 20:09

StÃ©phane Chazelas

283k53521856

answered Aug 29 at 19:26

ThoriumBR

1984

Thanks. This is simple and works exactly like I want it to.
â€“Â Kliwer
Aug 29 at 19:39

3

It's sad that this is marked as the solution because it doesn't even answer the question, which is what everyone will expect to find when they come here in the future with the same question. Maybe the question should be changed to reflect that OP doesn't actually care about what it returns.
â€“Â pipe
Aug 30 at 9:28

You are right, it does not answers the question, but it solves OP problem. Is tailored for this only case, but that's all OP wants - solve his problem.
â€“Â ThoriumBR
Aug 30 at 11:43

add a commentÂ |Â

up vote
8
down vote

accepted

You could use var=$(echo "$versionfull.0" | cut -d'.' -f3).

In the first case, versionfull will contain 6.40.4.0, ignoring the padding and returning 4 as needed. In the second case, the .0 will be padded and returned.

edited Aug 29 at 20:09

StÃ©phane Chazelas

283k53521856

answered Aug 29 at 19:26

ThoriumBR

1984

You could use var=$(echo "$versionfull.0" | cut -d'.' -f3).

In the first case, versionfull will contain 6.40.4.0, ignoring the padding and returning 4 as needed. In the second case, the .0 will be padded and returned.

edited Aug 29 at 20:09

StÃ©phane Chazelas

283k53521856

answered Aug 29 at 19:26

ThoriumBR

1984

edited Aug 29 at 20:09

StÃ©phane Chazelas

283k53521856

edited Aug 29 at 20:09

StÃ©phane Chazelas

283k53521856

edited Aug 29 at 20:09

StÃ©phane Chazelas

283k53521856

answered Aug 29 at 19:26

ThoriumBR

1984

answered Aug 29 at 19:26

ThoriumBR

1984

answered Aug 29 at 19:26

ThoriumBR

1984

Thanks. This is simple and works exactly like I want it to.
â€“Â Kliwer
Aug 29 at 19:39

3

It's sad that this is marked as the solution because it doesn't even answer the question, which is what everyone will expect to find when they come here in the future with the same question. Maybe the question should be changed to reflect that OP doesn't actually care about what it returns.
â€“Â pipe
Aug 30 at 9:28

You are right, it does not answers the question, but it solves OP problem. Is tailored for this only case, but that's all OP wants - solve his problem.
â€“Â ThoriumBR
Aug 30 at 11:43

add a commentÂ |Â

Thanks. This is simple and works exactly like I want it to.
â€“Â Kliwer
Aug 29 at 19:39

3

It's sad that this is marked as the solution because it doesn't even answer the question, which is what everyone will expect to find when they come here in the future with the same question. Maybe the question should be changed to reflect that OP doesn't actually care about what it returns.
â€“Â pipe
Aug 30 at 9:28

You are right, it does not answers the question, but it solves OP problem. Is tailored for this only case, but that's all OP wants - solve his problem.
â€“Â ThoriumBR
Aug 30 at 11:43

Thanks. This is simple and works exactly like I want it to.
â€“Â Kliwer
Aug 29 at 19:39

It's sad that this is marked as the solution because it doesn't even answer the question, which is what everyone will expect to find when they come here in the future with the same question. Maybe the question should be changed to reflect that OP doesn't actually care about what it returns.
â€“Â pipe
Aug 30 at 9:28

You are right, it does not answers the question, but it solves OP problem. Is tailored for this only case, but that's all OP wants - solve his problem.
â€“Â ThoriumBR
Aug 30 at 11:43

add a commentÂ |Â

up vote
10
down vote

To answer your direct question, cut returns nothing except a trailing newline, as per the spec (thanks to don_crissti for that reference):

echo "$versionfull" | cut -d. -f3 | od -c
0000000 n
0000001

If you have a shell that supports here-strings, you could do the following:

IFS=. read a b c <<< "$versionfull"

Notice the quoting for $versionfull, in case it ever had whitespace (anything from $IFS).

If you think that c might be empty, then ask to set it to zero:

c=$c:-0

edited Aug 29 at 19:49

answered Aug 29 at 19:27

Jeff Schaller

32.1k849109

2

Note that the need to quote in IFS=. read a b c <<< "$versionfull" was only for older versions of bash; other shells and newer versions of bash don't have the problem.
â€“Â StÃ©phane Chazelas
Aug 29 at 19:43

Note that if the input has only one field, cut returns that field.
â€“Â StÃ©phane Chazelas
Aug 29 at 20:05

add a commentÂ |Â

up vote
10
down vote

To answer your direct question, cut returns nothing except a trailing newline, as per the spec (thanks to don_crissti for that reference):

echo "$versionfull" | cut -d. -f3 | od -c
0000000 n
0000001

If you have a shell that supports here-strings, you could do the following:

IFS=. read a b c <<< "$versionfull"

Notice the quoting for $versionfull, in case it ever had whitespace (anything from $IFS).

If you think that c might be empty, then ask to set it to zero:

c=$c:-0

edited Aug 29 at 19:49

answered Aug 29 at 19:27

Jeff Schaller

32.1k849109

2

Note that the need to quote in IFS=. read a b c <<< "$versionfull" was only for older versions of bash; other shells and newer versions of bash don't have the problem.
â€“Â StÃ©phane Chazelas
Aug 29 at 19:43

Note that if the input has only one field, cut returns that field.
â€“Â StÃ©phane Chazelas
Aug 29 at 20:05

add a commentÂ |Â

up vote
10
down vote

To answer your direct question, cut returns nothing except a trailing newline, as per the spec (thanks to don_crissti for that reference):

echo "$versionfull" | cut -d. -f3 | od -c
0000000 n
0000001

If you have a shell that supports here-strings, you could do the following:

IFS=. read a b c <<< "$versionfull"

Notice the quoting for $versionfull, in case it ever had whitespace (anything from $IFS).

If you think that c might be empty, then ask to set it to zero:

c=$c:-0

edited Aug 29 at 19:49

answered Aug 29 at 19:27

Jeff Schaller

32.1k849109

To answer your direct question, cut returns nothing except a trailing newline, as per the spec (thanks to don_crissti for that reference):

echo "$versionfull" | cut -d. -f3 | od -c
0000000 n
0000001

If you have a shell that supports here-strings, you could do the following:

IFS=. read a b c <<< "$versionfull"

Notice the quoting for $versionfull, in case it ever had whitespace (anything from $IFS).

If you think that c might be empty, then ask to set it to zero:

c=$c:-0

edited Aug 29 at 19:49

answered Aug 29 at 19:27

Jeff Schaller

32.1k849109

edited Aug 29 at 19:49

answered Aug 29 at 19:27

Jeff Schaller

32.1k849109

answered Aug 29 at 19:27

Jeff Schaller

32.1k849109

answered Aug 29 at 19:27

Jeff Schaller

32.1k849109

2

Note that the need to quote in IFS=. read a b c <<< "$versionfull" was only for older versions of bash; other shells and newer versions of bash don't have the problem.
â€“Â StÃ©phane Chazelas
Aug 29 at 19:43

Note that if the input has only one field, cut returns that field.
â€“Â StÃ©phane Chazelas
Aug 29 at 20:05

add a commentÂ |Â

2

Note that the need to quote in IFS=. read a b c <<< "$versionfull" was only for older versions of bash; other shells and newer versions of bash don't have the problem.
â€“Â StÃ©phane Chazelas
Aug 29 at 19:43

Note that if the input has only one field, cut returns that field.
â€“Â StÃ©phane Chazelas
Aug 29 at 20:05

Note that the need to quote in IFS=. read a b c <<< "$versionfull" was only for older versions of bash; other shells and newer versions of bash don't have the problem.
â€“Â StÃ©phane Chazelas
Aug 29 at 19:43

Note that if the input has only one field, cut returns that field.
â€“Â StÃ©phane Chazelas
Aug 29 at 20:05

add a commentÂ |Â

up vote
6
down vote

cut has an odd API.

$ echo a.b.c | cut -d. -f3
c
$ echo a.b | cut -d. -f3

$ echo a | cut -d. -f3
a

So the answer to What does cut return if the specified field does not exist? is either the first field or an empty field depending on whether the input line has one field or more.

$ echo a | cut -sd. -f2
$ echo a | cut -sd. -f1
$

(you asked for the first field, the input has only one field, but you don't get any output because the input has no delimiter).

So @ThoriumBR's suggestion to add a .0 is a very good one. Without it:

versionfull=5
echo "$versionfull" | cut -d. -f3

would actually output 5. By adding .0, we make sure the input has at least one delimiter. I would go further and use:

echo "$versionfull.0.0" | cut -d. -f3

To make sure the input has at least 3 fields.

edited Aug 30 at 6:40

answered Aug 29 at 20:02

283k53521856

The probability of version 7 in Mikrotik is low ;) Anyway, thanks - I'll do that.
â€“Â Kliwer
Aug 29 at 20:11

How does this relate to his second case? The input has a delimiter.
â€“Â Barmar
Aug 29 at 22:59

add a commentÂ |Â

up vote
6
down vote

cut has an odd API.

$ echo a.b.c | cut -d. -f3
c
$ echo a.b | cut -d. -f3

$ echo a | cut -d. -f3
a

So the answer to What does cut return if the specified field does not exist? is either the first field or an empty field depending on whether the input line has one field or more.

$ echo a | cut -sd. -f2
$ echo a | cut -sd. -f1
$

(you asked for the first field, the input has only one field, but you don't get any output because the input has no delimiter).

So @ThoriumBR's suggestion to add a .0 is a very good one. Without it:

versionfull=5
echo "$versionfull" | cut -d. -f3

would actually output 5. By adding .0, we make sure the input has at least one delimiter. I would go further and use:

echo "$versionfull.0.0" | cut -d. -f3

To make sure the input has at least 3 fields.

edited Aug 30 at 6:40

answered Aug 29 at 20:02

283k53521856

The probability of version 7 in Mikrotik is low ;) Anyway, thanks - I'll do that.
â€“Â Kliwer
Aug 29 at 20:11

How does this relate to his second case? The input has a delimiter.
â€“Â Barmar
Aug 29 at 22:59

add a commentÂ |Â

up vote
6
down vote

cut has an odd API.

$ echo a.b.c | cut -d. -f3
c
$ echo a.b | cut -d. -f3

$ echo a | cut -d. -f3
a

So the answer to What does cut return if the specified field does not exist? is either the first field or an empty field depending on whether the input line has one field or more.

$ echo a | cut -sd. -f2
$ echo a | cut -sd. -f1
$

(you asked for the first field, the input has only one field, but you don't get any output because the input has no delimiter).

So @ThoriumBR's suggestion to add a .0 is a very good one. Without it:

versionfull=5
echo "$versionfull" | cut -d. -f3

would actually output 5. By adding .0, we make sure the input has at least one delimiter. I would go further and use:

echo "$versionfull.0.0" | cut -d. -f3

To make sure the input has at least 3 fields.

edited Aug 30 at 6:40

answered Aug 29 at 20:02

283k53521856

cut has an odd API.

$ echo a.b.c | cut -d. -f3
c
$ echo a.b | cut -d. -f3

$ echo a | cut -d. -f3
a

So the answer to What does cut return if the specified field does not exist? is either the first field or an empty field depending on whether the input line has one field or more.

$ echo a | cut -sd. -f2
$ echo a | cut -sd. -f1
$

(you asked for the first field, the input has only one field, but you don't get any output because the input has no delimiter).

So @ThoriumBR's suggestion to add a .0 is a very good one. Without it:

versionfull=5
echo "$versionfull" | cut -d. -f3

would actually output 5. By adding .0, we make sure the input has at least one delimiter. I would go further and use:

echo "$versionfull.0.0" | cut -d. -f3

To make sure the input has at least 3 fields.

edited Aug 30 at 6:40

answered Aug 29 at 20:02

283k53521856

edited Aug 30 at 6:40

answered Aug 29 at 20:02

283k53521856

answered Aug 29 at 20:02

283k53521856

answered Aug 29 at 20:02

283k53521856

The probability of version 7 in Mikrotik is low ;) Anyway, thanks - I'll do that.
â€“Â Kliwer
Aug 29 at 20:11

How does this relate to his second case? The input has a delimiter.
â€“Â Barmar
Aug 29 at 22:59

add a commentÂ |Â

The probability of version 7 in Mikrotik is low ;) Anyway, thanks - I'll do that.
â€“Â Kliwer
Aug 29 at 20:11

How does this relate to his second case? The input has a delimiter.
â€“Â Barmar
Aug 29 at 22:59

The probability of version 7 in Mikrotik is low ;) Anyway, thanks - I'll do that.
â€“Â Kliwer
Aug 29 at 20:11

How does this relate to his second case? The input has a delimiter.
â€“Â Barmar
Aug 29 at 22:59

add a commentÂ |Â

up vote
1
down vote

It sets it to an empty string. You should quote the variable when using it with the [ command.

if [ "$var" == "" ]
then echo "Var is empty"
fi

Without the quotes, the first line expands to:

if [ == "" ]

which is invalid syntax because == requires a parameter to the left of it.

answered Aug 29 at 23:03

Barmar

6,7201122

add a commentÂ |Â

up vote
1
down vote

It sets it to an empty string. You should quote the variable when using it with the [ command.

if [ "$var" == "" ]
then echo "Var is empty"
fi

Without the quotes, the first line expands to:

if [ == "" ]

which is invalid syntax because == requires a parameter to the left of it.

answered Aug 29 at 23:03

Barmar

6,7201122

add a commentÂ |Â

up vote
1
down vote

It sets it to an empty string. You should quote the variable when using it with the [ command.

if [ "$var" == "" ]
then echo "Var is empty"
fi

Without the quotes, the first line expands to:

if [ == "" ]

which is invalid syntax because == requires a parameter to the left of it.

answered Aug 29 at 23:03

Barmar

6,7201122

It sets it to an empty string. You should quote the variable when using it with the [ command.

if [ "$var" == "" ]
then echo "Var is empty"
fi

Without the quotes, the first line expands to:

if [ == "" ]

which is invalid syntax because == requires a parameter to the left of it.

answered Aug 29 at 23:03

Barmar

6,7201122

answered Aug 29 at 23:03

Barmar

6,7201122

answered Aug 29 at 23:03

Barmar

6,7201122

answered Aug 29 at 23:03

Barmar

6,7201122

add a commentÂ |Â

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