Awk doesn't exit despite “exit 0” command
I have the following command:
sudo docker logs -f <id> | awk '/Listening on / {print $3; exit 0;}'
From what I understand, awk should find the first line that matches the pattern, print the correct column, and exit. However, this does not always happen: most the time it simply prints the correct column and hangs, although occasionally it exits correctly.
I've tried
$ sudo stdbuf -i0 -o0 -e0 docker logs ... # hangs
$ sudo docker logs ... | cat | awk ... # hangs
In trying to produce a minimal example, I also tried making a pipe using mkfifo, and using cat foo | awk ... but that doesn't hang.
The output from docker logs -f <id> is
Listening on 172.17.0.2/16
...
and then it remains open, but doesn't write any thing else.
I don't understand what's going on--does anyone have any ideas?
awk pipe docker coreutils
edited Dec 17 at 22:51
Jeff Schaller
38.7k1053125
asked Dec 17 at 22:07
user60561
1355
add a comment |
I have the following command:
sudo docker logs -f <id> | awk '/Listening on / {print $3; exit 0;}'
From what I understand, awk should find the first line that matches the pattern, print the correct column, and exit. However, this does not always happen: most the time it simply prints the correct column and hangs, although occasionally it exits correctly.
I've tried
$ sudo stdbuf -i0 -o0 -e0 docker logs ... # hangs
$ sudo docker logs ... | cat | awk ... # hangs
In trying to produce a minimal example, I also tried making a pipe using mkfifo, and using cat foo | awk ... but that doesn't hang.
The output from docker logs -f <id> is
Listening on 172.17.0.2/16
...
and then it remains open, but doesn't write any thing else.
I don't understand what's going on--does anyone have any ideas?
awk pipe docker coreutils
edited Dec 17 at 22:51
Jeff Schaller
38.7k1053125
asked Dec 17 at 22:07
user60561
1355
Unable to replicate:for i in {10..20}; do echo $i; done | awk '{ exit 0} END { print NR}'works as apparently intended.
– DopeGhoti
Dec 17 at 22:43
1
Similar: How to print only one match of grep when tail -f? or Grep slow to exit after finding match? or make tail -f exit on a broken pipe. Most likelyawkexits but your shell is waiting for all processes in the pipeline.
– Stéphane Chazelas
Dec 17 at 22:44
Your output above indicates docker logs is emitting terminal sequences; are you certain that it isn’t when you pipe it to awk? Maybe pipe it into hexdump just to have a peek.
– mevets
Dec 17 at 23:31
@mevets I assume you're referring to the syntax highlighting? StackExchange is doing that, the output is plain text.
– user60561
Dec 18 at 14:23
add a comment |
I have the following command:
sudo docker logs -f <id> | awk '/Listening on / {print $3; exit 0;}'
From what I understand, awk should find the first line that matches the pattern, print the correct column, and exit. However, this does not always happen: most the time it simply prints the correct column and hangs, although occasionally it exits correctly.
I've tried
$ sudo stdbuf -i0 -o0 -e0 docker logs ... # hangs
$ sudo docker logs ... | cat | awk ... # hangs
In trying to produce a minimal example, I also tried making a pipe using mkfifo, and using cat foo | awk ... but that doesn't hang.
The output from docker logs -f <id> is
Listening on 172.17.0.2/16
...
and then it remains open, but doesn't write any thing else.
I don't understand what's going on--does anyone have any ideas?
awk pipe docker coreutils
edited Dec 17 at 22:51
Jeff Schaller
38.7k1053125
asked Dec 17 at 22:07
user60561
1355
I have the following command:
sudo docker logs -f <id> | awk '/Listening on / {print $3; exit 0;}'
From what I understand, awk should find the first line that matches the pattern, print the correct column, and exit. However, this does not always happen: most the time it simply prints the correct column and hangs, although occasionally it exits correctly.
I've tried
$ sudo stdbuf -i0 -o0 -e0 docker logs ... # hangs
$ sudo docker logs ... | cat | awk ... # hangs
In trying to produce a minimal example, I also tried making a pipe using mkfifo, and using cat foo | awk ... but that doesn't hang.
The output from docker logs -f <id> is
Listening on 172.17.0.2/16
...
and then it remains open, but doesn't write any thing else.
I don't understand what's going on--does anyone have any ideas?
awk pipe docker coreutils
awk pipe docker coreutils
edited Dec 17 at 22:51
Jeff Schaller
38.7k1053125
asked Dec 17 at 22:07
user60561
1355
edited Dec 17 at 22:51
Jeff Schaller
38.7k1053125
asked Dec 17 at 22:07
user60561
1355
edited Dec 17 at 22:51
Jeff Schaller
38.7k1053125
edited Dec 17 at 22:51
Jeff Schaller
38.7k1053125
edited Dec 17 at 22:51
Jeff Schaller
38.7k1053125
38.7k1053125
asked Dec 17 at 22:07
user60561
1355
asked Dec 17 at 22:07
user60561
1355
asked Dec 17 at 22:07
user60561
1355
1355
Unable to replicate:for i in {10..20}; do echo $i; done | awk '{ exit 0} END { print NR}'works as apparently intended.
– DopeGhoti
Dec 17 at 22:43
1
Similar: How to print only one match of grep when tail -f? or Grep slow to exit after finding match? or make tail -f exit on a broken pipe. Most likelyawkexits but your shell is waiting for all processes in the pipeline.
– Stéphane Chazelas
Dec 17 at 22:44
Your output above indicates docker logs is emitting terminal sequences; are you certain that it isn’t when you pipe it to awk? Maybe pipe it into hexdump just to have a peek.
– mevets
Dec 17 at 23:31
@mevets I assume you're referring to the syntax highlighting? StackExchange is doing that, the output is plain text.
– user60561
Dec 18 at 14:23
add a comment |
Unable to replicate:for i in {10..20}; do echo $i; done | awk '{ exit 0} END { print NR}'works as apparently intended.
– DopeGhoti
Dec 17 at 22:43
1
Similar: How to print only one match of grep when tail -f? or Grep slow to exit after finding match? or make tail -f exit on a broken pipe. Most likelyawkexits but your shell is waiting for all processes in the pipeline.
– Stéphane Chazelas
Dec 17 at 22:44
Your output above indicates docker logs is emitting terminal sequences; are you certain that it isn’t when you pipe it to awk? Maybe pipe it into hexdump just to have a peek.
– mevets
Dec 17 at 23:31
@mevets I assume you're referring to the syntax highlighting? StackExchange is doing that, the output is plain text.
– user60561
Dec 18 at 14:23
Unable to replicate:
for i in {10..20}; do echo $i; done | awk '{ exit 0} END { print NR}' works as apparently intended.– DopeGhoti
Dec 17 at 22:43
Unable to replicate:
for i in {10..20}; do echo $i; done | awk '{ exit 0} END { print NR}' works as apparently intended.– DopeGhoti
Dec 17 at 22:43
1
1
Similar: How to print only one match of grep when tail -f? or Grep slow to exit after finding match? or make tail -f exit on a broken pipe. Most likely
awk exits but your shell is waiting for all processes in the pipeline.– Stéphane Chazelas
Dec 17 at 22:44
Similar: How to print only one match of grep when tail -f? or Grep slow to exit after finding match? or make tail -f exit on a broken pipe. Most likely
awk exits but your shell is waiting for all processes in the pipeline.– Stéphane Chazelas
Dec 17 at 22:44
Your output above indicates docker logs is emitting terminal sequences; are you certain that it isn’t when you pipe it to awk? Maybe pipe it into hexdump just to have a peek.
– mevets
Dec 17 at 23:31
Your output above indicates docker logs is emitting terminal sequences; are you certain that it isn’t when you pipe it to awk? Maybe pipe it into hexdump just to have a peek.
– mevets
Dec 17 at 23:31
@mevets I assume you're referring to the syntax highlighting? StackExchange is doing that, the output is plain text.
– user60561
Dec 18 at 14:23
@mevets I assume you're referring to the syntax highlighting? StackExchange is doing that, the output is plain text.
– user60561
Dec 18 at 14:23
add a comment |
1 Answer
1
active
oldest
votes
From man bash:
The shell waits for all commands in the pipeline to terminate before
returning a value.
I don't have docker installed but maybe try this:
awk '/Listening on / {print $3; exit 0;}' <( sudo docker logs -f <id> )
Or you could try this:
sudo docker logs -f <id> | (awk '/Listening on / {print $3; exit 0;}'; pkill -P $$ )
So perhaps an explanation of what is going on would help. I'm assuming that the 'docker logs' command does not normally exit (the -f == follow?).
The original problem arises because the pipeline is not exiting on awk's termination - this is because the pipeline is still waiting on the docker program (see my extract above from the bash man page).
The pkill simply kills anything that has parent id $$ - ie at that moment, that is just docker.
Obviously, it would not be a good idea to chuck that command into background with '&' and then run other things - they would also get killed!
answered Dec 17 at 23:13
wef
913
Yup, this is exactly it! This behavior is surprising, although not unexpected--the only way it could work otherwise is if bash sent SIGINT or SIGQUIT to the other programs in the pipe, and I've never seen that happen. Thank you!
– user60561
Dec 18 at 14:25
add a comment |
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1 Answer
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From man bash:
The shell waits for all commands in the pipeline to terminate before
returning a value.
I don't have docker installed but maybe try this:
awk '/Listening on / {print $3; exit 0;}' <( sudo docker logs -f <id> )
Or you could try this:
sudo docker logs -f <id> | (awk '/Listening on / {print $3; exit 0;}'; pkill -P $$ )
So perhaps an explanation of what is going on would help. I'm assuming that the 'docker logs' command does not normally exit (the -f == follow?).
The original problem arises because the pipeline is not exiting on awk's termination - this is because the pipeline is still waiting on the docker program (see my extract above from the bash man page).
The pkill simply kills anything that has parent id $$ - ie at that moment, that is just docker.
Obviously, it would not be a good idea to chuck that command into background with '&' and then run other things - they would also get killed!
answered Dec 17 at 23:13
wef
913
Yup, this is exactly it! This behavior is surprising, although not unexpected--the only way it could work otherwise is if bash sent SIGINT or SIGQUIT to the other programs in the pipe, and I've never seen that happen. Thank you!
– user60561
Dec 18 at 14:25
add a comment |
From man bash:
The shell waits for all commands in the pipeline to terminate before
returning a value.
I don't have docker installed but maybe try this:
awk '/Listening on / {print $3; exit 0;}' <( sudo docker logs -f <id> )
Or you could try this:
sudo docker logs -f <id> | (awk '/Listening on / {print $3; exit 0;}'; pkill -P $$ )
So perhaps an explanation of what is going on would help. I'm assuming that the 'docker logs' command does not normally exit (the -f == follow?).
The original problem arises because the pipeline is not exiting on awk's termination - this is because the pipeline is still waiting on the docker program (see my extract above from the bash man page).
The pkill simply kills anything that has parent id $$ - ie at that moment, that is just docker.
Obviously, it would not be a good idea to chuck that command into background with '&' and then run other things - they would also get killed!
answered Dec 17 at 23:13
wef
913
Yup, this is exactly it! This behavior is surprising, although not unexpected--the only way it could work otherwise is if bash sent SIGINT or SIGQUIT to the other programs in the pipe, and I've never seen that happen. Thank you!
– user60561
Dec 18 at 14:25
add a comment |
From man bash:
The shell waits for all commands in the pipeline to terminate before
returning a value.
I don't have docker installed but maybe try this:
awk '/Listening on / {print $3; exit 0;}' <( sudo docker logs -f <id> )
Or you could try this:
sudo docker logs -f <id> | (awk '/Listening on / {print $3; exit 0;}'; pkill -P $$ )
So perhaps an explanation of what is going on would help. I'm assuming that the 'docker logs' command does not normally exit (the -f == follow?).
The original problem arises because the pipeline is not exiting on awk's termination - this is because the pipeline is still waiting on the docker program (see my extract above from the bash man page).
The pkill simply kills anything that has parent id $$ - ie at that moment, that is just docker.
Obviously, it would not be a good idea to chuck that command into background with '&' and then run other things - they would also get killed!
answered Dec 17 at 23:13
wef
913
From man bash:
The shell waits for all commands in the pipeline to terminate before
returning a value.
I don't have docker installed but maybe try this:
awk '/Listening on / {print $3; exit 0;}' <( sudo docker logs -f <id> )
Or you could try this:
sudo docker logs -f <id> | (awk '/Listening on / {print $3; exit 0;}'; pkill -P $$ )
So perhaps an explanation of what is going on would help. I'm assuming that the 'docker logs' command does not normally exit (the -f == follow?).
The original problem arises because the pipeline is not exiting on awk's termination - this is because the pipeline is still waiting on the docker program (see my extract above from the bash man page).
The pkill simply kills anything that has parent id $$ - ie at that moment, that is just docker.
Obviously, it would not be a good idea to chuck that command into background with '&' and then run other things - they would also get killed!
answered Dec 17 at 23:13
wef
913
edited Dec 18 at 1:24
answered Dec 17 at 23:13
wef
913
answered Dec 17 at 23:13
wef
913
answered Dec 17 at 23:13
wef
913
913
Yup, this is exactly it! This behavior is surprising, although not unexpected--the only way it could work otherwise is if bash sent SIGINT or SIGQUIT to the other programs in the pipe, and I've never seen that happen. Thank you!
– user60561
Dec 18 at 14:25
add a comment |
Yup, this is exactly it! This behavior is surprising, although not unexpected--the only way it could work otherwise is if bash sent SIGINT or SIGQUIT to the other programs in the pipe, and I've never seen that happen. Thank you!
– user60561
Dec 18 at 14:25
Yup, this is exactly it! This behavior is surprising, although not unexpected--the only way it could work otherwise is if bash sent SIGINT or SIGQUIT to the other programs in the pipe, and I've never seen that happen. Thank you!
– user60561
Dec 18 at 14:25
Yup, this is exactly it! This behavior is surprising, although not unexpected--the only way it could work otherwise is if bash sent SIGINT or SIGQUIT to the other programs in the pipe, and I've never seen that happen. Thank you!
– user60561
Dec 18 at 14:25
add a comment |
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Unable to replicate:
for i in {10..20}; do echo $i; done | awk '{ exit 0} END { print NR}'works as apparently intended.– DopeGhoti
Dec 17 at 22:43
1
Similar: How to print only one match of grep when tail -f? or Grep slow to exit after finding match? or make tail -f exit on a broken pipe. Most likely
awkexits but your shell is waiting for all processes in the pipeline.– Stéphane Chazelas
Dec 17 at 22:44
Your output above indicates docker logs is emitting terminal sequences; are you certain that it isn’t when you pipe it to awk? Maybe pipe it into hexdump just to have a peek.
– mevets
Dec 17 at 23:31
@mevets I assume you're referring to the syntax highlighting? StackExchange is doing that, the output is plain text.
– user60561
Dec 18 at 14:23