How can I use sed to edit bash debug output? (bash -x)

up vote
2
down vote

favorite

#!/bin/bash -x
echo This is a script that has debugging turned on

This script outputs

+ echo This is a script that has debugging turned on
This is a script that has debugging turned on

I want to get rid of these +'s by deleting them or replacing them. I expected sed could fix my problem (sed 's/^++//g') -- But this approach doesn't affect the debug output lines.

With some more experimenting, I discovered that the debug output seems to be getting written to stderr (inferred this with the command ./test.sh 2>/dev/null which the output then excludes the debug lines)

With this new information, I would expect this to work
./test.sh 2>&1 | sed 's/^++//g'

But, alas, I still get the same undesired output:

+ echo This is a script that has debugging turned on
This is a script that has debugging turned on

asked 1 hour ago

aitee

111

New contributor

2

Why are you working so hard to undo what -x has added? Why not just remove the -x?
â€“Â Jeff Schaller
1 hour ago

add a commentÂ |Â

up vote
2
down vote

favorite

#!/bin/bash -x
echo This is a script that has debugging turned on

This script outputs

+ echo This is a script that has debugging turned on
This is a script that has debugging turned on

I want to get rid of these +'s by deleting them or replacing them. I expected sed could fix my problem (sed 's/^++//g') -- But this approach doesn't affect the debug output lines.

With this new information, I would expect this to work
./test.sh 2>&1 | sed 's/^++//g'

But, alas, I still get the same undesired output:

+ echo This is a script that has debugging turned on
This is a script that has debugging turned on

asked 1 hour ago

aitee

111

New contributor

2

Why are you working so hard to undo what -x has added? Why not just remove the -x?
â€“Â Jeff Schaller
1 hour ago

add a commentÂ |Â

up vote
2
down vote

favorite

#!/bin/bash -x
echo This is a script that has debugging turned on

This script outputs

+ echo This is a script that has debugging turned on
This is a script that has debugging turned on

I want to get rid of these +'s by deleting them or replacing them. I expected sed could fix my problem (sed 's/^++//g') -- But this approach doesn't affect the debug output lines.

With this new information, I would expect this to work
./test.sh 2>&1 | sed 's/^++//g'

But, alas, I still get the same undesired output:

+ echo This is a script that has debugging turned on
This is a script that has debugging turned on

asked 1 hour ago

aitee

111

New contributor

#!/bin/bash -x
echo This is a script that has debugging turned on

This script outputs

+ echo This is a script that has debugging turned on
This is a script that has debugging turned on

I want to get rid of these +'s by deleting them or replacing them. I expected sed could fix my problem (sed 's/^++//g') -- But this approach doesn't affect the debug output lines.

With this new information, I would expect this to work
./test.sh 2>&1 | sed 's/^++//g'

But, alas, I still get the same undesired output:

+ echo This is a script that has debugging turned on
This is a script that has debugging turned on

bash sed scripting stderr

asked 1 hour ago

aitee

111

New contributor

asked 1 hour ago

aitee

111

New contributor

asked 1 hour ago

aitee

111

New contributor

asked 1 hour ago

aitee

111

asked 1 hour ago

aitee

111

New contributor

aitee is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

2

Why are you working so hard to undo what -x has added? Why not just remove the -x?
â€“Â Jeff Schaller
1 hour ago

add a commentÂ |Â

2

Why are you working so hard to undo what -x has added? Why not just remove the -x?
â€“Â Jeff Schaller
1 hour ago

Why are you working so hard to undo what -x has added? Why not just remove the -x?
â€“Â Jeff Schaller
1 hour ago

add a commentÂ |Â

3 Answers
3

active

oldest

votes

up vote
3
down vote

The + is the PS4 prompt. Set it to an empty string:

#!/bin/bash

PS4=''
set -x

echo 'This is a script that has debugging turned on'

Testing:

$ bash script.sh
echo 'This is a script that has debugging turned on'
This is a script that has debugging turned on

Or, with your original script, set PS4 to an empty string for the script when invoking it:

$ PS4='' ./script.sh
echo This is a script that has debugging turned on
This is a script that has debugging turned on

This could be used to insert a timestamp:

$ PS4='$(date +"%T: ")' ./script.sh
21:08:19: echo 'This is a script that has debugging turned on'
This is a script that has debugging turned on
21:08:19: echo 'Now sleeping for 2 seconds'
Now sleeping for 2 seconds
21:08:19: sleep 2
21:08:21: echo Done
Done

edited 32 mins ago

answered 38 mins ago

Kusalananda

111k15216341

add a commentÂ |Â

up vote
2
down vote

The main limitation you're running into is that + is an extended regular expression feature, so you'll need to enable extended regular expression functionality; with most seds, that's with the -E flag:

./test.sh 2>&1 | sed -E 's/^++ //'

I made two other changes:

added a trailing space, so that debugged commands show up left-aligned

removed the /g flag, since the regex is anchored, there can be only one match per line

edited 1 hour ago

don_crissti

48.1k15127157

answered 1 hour ago

Jeff Schaller

34.3k951114

Note that once you commingle stdout and stderr, any actual (stdout) output with leading plus signs will also be stripped.
â€“Â Jeff Schaller
1 hour ago

add a commentÂ |Â

up vote
1
down vote

You can redirect stderr into a process substitution. However that may affect the order of the output:

$ bash -x -c 'hostname; echo "$(date)"'
+ hostname
jackmanVM
++ date
+ echo 'Tue Oct 23 15:22:02 EDT 2018'
Tue Oct 23 15:22:02 EDT 2018

$ bash -x -c 'hostname; echo "$(date)"' 2> >(sed -E 's/^++/debug: /')
debug: hostname
jackmanVM
debug: date
Tue Oct 23 15:22:35 EDT 2018
debug: echo 'Tue Oct 23 15:22:35 EDT 2018'

answered 20 mins ago

glenn jackman

49.2k469106

add a commentÂ |Â

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3 Answers
3

active

oldest

votes

3 Answers
3

active

oldest

votes

up vote
3
down vote

The + is the PS4 prompt. Set it to an empty string:

#!/bin/bash

PS4=''
set -x

echo 'This is a script that has debugging turned on'

Testing:

$ bash script.sh
echo 'This is a script that has debugging turned on'
This is a script that has debugging turned on

Or, with your original script, set PS4 to an empty string for the script when invoking it:

$ PS4='' ./script.sh
echo This is a script that has debugging turned on
This is a script that has debugging turned on

This could be used to insert a timestamp:

$ PS4='$(date +"%T: ")' ./script.sh
21:08:19: echo 'This is a script that has debugging turned on'
This is a script that has debugging turned on
21:08:19: echo 'Now sleeping for 2 seconds'
Now sleeping for 2 seconds
21:08:19: sleep 2
21:08:21: echo Done
Done

edited 32 mins ago

answered 38 mins ago

Kusalananda

111k15216341

add a commentÂ |Â

up vote
3
down vote

The + is the PS4 prompt. Set it to an empty string:

#!/bin/bash

PS4=''
set -x

echo 'This is a script that has debugging turned on'

Testing:

$ bash script.sh
echo 'This is a script that has debugging turned on'
This is a script that has debugging turned on

Or, with your original script, set PS4 to an empty string for the script when invoking it:

$ PS4='' ./script.sh
echo This is a script that has debugging turned on
This is a script that has debugging turned on

This could be used to insert a timestamp:

$ PS4='$(date +"%T: ")' ./script.sh
21:08:19: echo 'This is a script that has debugging turned on'
This is a script that has debugging turned on
21:08:19: echo 'Now sleeping for 2 seconds'
Now sleeping for 2 seconds
21:08:19: sleep 2
21:08:21: echo Done
Done

edited 32 mins ago

answered 38 mins ago

Kusalananda

111k15216341

add a commentÂ |Â

up vote
3
down vote

The + is the PS4 prompt. Set it to an empty string:

#!/bin/bash

PS4=''
set -x

echo 'This is a script that has debugging turned on'

Testing:

$ bash script.sh
echo 'This is a script that has debugging turned on'
This is a script that has debugging turned on

Or, with your original script, set PS4 to an empty string for the script when invoking it:

$ PS4='' ./script.sh
echo This is a script that has debugging turned on
This is a script that has debugging turned on

This could be used to insert a timestamp:

$ PS4='$(date +"%T: ")' ./script.sh
21:08:19: echo 'This is a script that has debugging turned on'
This is a script that has debugging turned on
21:08:19: echo 'Now sleeping for 2 seconds'
Now sleeping for 2 seconds
21:08:19: sleep 2
21:08:21: echo Done
Done

edited 32 mins ago

answered 38 mins ago

Kusalananda

111k15216341

The + is the PS4 prompt. Set it to an empty string:

#!/bin/bash

PS4=''
set -x

echo 'This is a script that has debugging turned on'

Testing:

$ bash script.sh
echo 'This is a script that has debugging turned on'
This is a script that has debugging turned on

Or, with your original script, set PS4 to an empty string for the script when invoking it:

$ PS4='' ./script.sh
echo This is a script that has debugging turned on
This is a script that has debugging turned on

This could be used to insert a timestamp:

$ PS4='$(date +"%T: ")' ./script.sh
21:08:19: echo 'This is a script that has debugging turned on'
This is a script that has debugging turned on
21:08:19: echo 'Now sleeping for 2 seconds'
Now sleeping for 2 seconds
21:08:19: sleep 2
21:08:21: echo Done
Done

edited 32 mins ago

answered 38 mins ago

Kusalananda

111k15216341

edited 32 mins ago

answered 38 mins ago

Kusalananda

111k15216341

answered 38 mins ago

Kusalananda

111k15216341

answered 38 mins ago

Kusalananda

111k15216341

add a commentÂ |Â

up vote
2
down vote

./test.sh 2>&1 | sed -E 's/^++ //'

I made two other changes:

added a trailing space, so that debugged commands show up left-aligned

removed the /g flag, since the regex is anchored, there can be only one match per line

edited 1 hour ago

don_crissti

48.1k15127157

answered 1 hour ago

Jeff Schaller

34.3k951114

Note that once you commingle stdout and stderr, any actual (stdout) output with leading plus signs will also be stripped.
â€“Â Jeff Schaller
1 hour ago

add a commentÂ |Â

up vote
2
down vote

./test.sh 2>&1 | sed -E 's/^++ //'

I made two other changes:

added a trailing space, so that debugged commands show up left-aligned

removed the /g flag, since the regex is anchored, there can be only one match per line

edited 1 hour ago

don_crissti

48.1k15127157

answered 1 hour ago

Jeff Schaller

34.3k951114

Note that once you commingle stdout and stderr, any actual (stdout) output with leading plus signs will also be stripped.
â€“Â Jeff Schaller
1 hour ago

add a commentÂ |Â

up vote
2
down vote

./test.sh 2>&1 | sed -E 's/^++ //'

I made two other changes:

added a trailing space, so that debugged commands show up left-aligned

removed the /g flag, since the regex is anchored, there can be only one match per line

edited 1 hour ago

don_crissti

48.1k15127157

answered 1 hour ago

Jeff Schaller

34.3k951114

./test.sh 2>&1 | sed -E 's/^++ //'

I made two other changes:

added a trailing space, so that debugged commands show up left-aligned

removed the /g flag, since the regex is anchored, there can be only one match per line

edited 1 hour ago

don_crissti

48.1k15127157

answered 1 hour ago

Jeff Schaller

34.3k951114

edited 1 hour ago

don_crissti

48.1k15127157

edited 1 hour ago

don_crissti

48.1k15127157

edited 1 hour ago

don_crissti

48.1k15127157

answered 1 hour ago

Jeff Schaller

34.3k951114

answered 1 hour ago

Jeff Schaller

34.3k951114

answered 1 hour ago

Jeff Schaller

34.3k951114

Note that once you commingle stdout and stderr, any actual (stdout) output with leading plus signs will also be stripped.
â€“Â Jeff Schaller
1 hour ago

add a commentÂ |Â

Note that once you commingle stdout and stderr, any actual (stdout) output with leading plus signs will also be stripped.
â€“Â Jeff Schaller
1 hour ago

Note that once you commingle stdout and stderr, any actual (stdout) output with leading plus signs will also be stripped.
â€“Â Jeff Schaller
1 hour ago

add a commentÂ |Â

up vote
1
down vote

You can redirect stderr into a process substitution. However that may affect the order of the output:

$ bash -x -c 'hostname; echo "$(date)"'
+ hostname
jackmanVM
++ date
+ echo 'Tue Oct 23 15:22:02 EDT 2018'
Tue Oct 23 15:22:02 EDT 2018

$ bash -x -c 'hostname; echo "$(date)"' 2> >(sed -E 's/^++/debug: /')
debug: hostname
jackmanVM
debug: date
Tue Oct 23 15:22:35 EDT 2018
debug: echo 'Tue Oct 23 15:22:35 EDT 2018'

answered 20 mins ago

glenn jackman

49.2k469106

add a commentÂ |Â

up vote
1
down vote

You can redirect stderr into a process substitution. However that may affect the order of the output:

$ bash -x -c 'hostname; echo "$(date)"'
+ hostname
jackmanVM
++ date
+ echo 'Tue Oct 23 15:22:02 EDT 2018'
Tue Oct 23 15:22:02 EDT 2018

$ bash -x -c 'hostname; echo "$(date)"' 2> >(sed -E 's/^++/debug: /')
debug: hostname
jackmanVM
debug: date
Tue Oct 23 15:22:35 EDT 2018
debug: echo 'Tue Oct 23 15:22:35 EDT 2018'

answered 20 mins ago

glenn jackman

49.2k469106

add a commentÂ |Â

up vote
1
down vote

You can redirect stderr into a process substitution. However that may affect the order of the output:

$ bash -x -c 'hostname; echo "$(date)"'
+ hostname
jackmanVM
++ date
+ echo 'Tue Oct 23 15:22:02 EDT 2018'
Tue Oct 23 15:22:02 EDT 2018

$ bash -x -c 'hostname; echo "$(date)"' 2> >(sed -E 's/^++/debug: /')
debug: hostname
jackmanVM
debug: date
Tue Oct 23 15:22:35 EDT 2018
debug: echo 'Tue Oct 23 15:22:35 EDT 2018'

answered 20 mins ago

glenn jackman

49.2k469106

You can redirect stderr into a process substitution. However that may affect the order of the output:

$ bash -x -c 'hostname; echo "$(date)"'
+ hostname
jackmanVM
++ date
+ echo 'Tue Oct 23 15:22:02 EDT 2018'
Tue Oct 23 15:22:02 EDT 2018

$ bash -x -c 'hostname; echo "$(date)"' 2> >(sed -E 's/^++/debug: /')
debug: hostname
jackmanVM
debug: date
Tue Oct 23 15:22:35 EDT 2018
debug: echo 'Tue Oct 23 15:22:35 EDT 2018'

answered 20 mins ago

glenn jackman

49.2k469106

answered 20 mins ago

glenn jackman

49.2k469106

answered 20 mins ago

glenn jackman

49.2k469106

answered 20 mins ago

glenn jackman

49.2k469106

add a commentÂ |Â

aitee is a new contributor. Be nice, and check out our Code of Conduct.

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