bash script/pgrep not working as expected

Question

I have a bash script that tries to call pgrep with arguments (Over simplified):

PATTERN="'/opt/apps/bin/lighttpd.bin -f /opt/apps/etc/lighttpd/lighttpd.conf\$'"
pgrep -f $PATTERN
echo pgrep -f $PATTERN

Gives the following output:

Usage: pgrep [-cflvx] [-d DELIM] [-n|-o] [-P PPIDLIST] [-g PGRPLIST] [-s SIDLIST]
        [-u EUIDLIST] [-U UIDLIST] [-G GIDLIST] [-t TERMLIST] [PATTERN]
pgrep -f '/opt/apps/bin/lighttpd.bin -f /opt/apps/etc/lighttpd/lighttpd.conf$'

I suppose it means the argument is not passed to pgrep but is passed to echo for some reason.

What I'm expecting:

7632
pgrep -f '/opt/apps/bin/lighttpd.bin -f /opt/apps/etc/lighttpd/lighttpd.conf$'

When I run the preg line by itself, it outputs 7632 as expected.

Am I doing something wrong here? I've tried with sh, dash and bash. Same outcomes, I really don't see the problem.

barti_ddu · Accepted Answer · 2012-02-20 17:32:11Z

3

You need to surround PATTERN in double quotes:

PATTERN="/opt/apps/bin/lighttpd.bin -f /opt/apps/etc/lighttpd/lighttpd.conf\$"
pgrep -f "$PATTERN"

See: quoting variables

Edit: and for echoing i would just do:

echo pgrep -f \'$PATTERN\'

edited Feb 20, 2012 at 17:32

answered Feb 20, 2012 at 16:44

barti_ddu

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3 Comments

Jonathan Leffler Over a year ago

+1 for double quoting and dropping the single quotes from inside the pattern string. However, you should probably point out the second change too.

alex Over a year ago

Edit: Sorry, stackoverflow submitted my comment instead of inserting a newline... Your solution works, thank you! Could you explain to me why '' works when I run the command at the prompt but in my script it requires "" ? Thank you

barti_ddu Over a year ago

@alex: this happens because PATTERN doesn't contain literal quote symbols after assignment (they rather indicate that whole expression is single string); to keep treating this expression as a single string, you need to quote it explicitly.

shellter · Accepted Answer · 2012-02-20 17:14:10Z

2

As I don't have lighttpd.bin available to test with, I am submitting an untested option, mostly agreeing with @barti_ddu, but with a slightly different twist

PATTERN='/opt/apps/bin/lighttpd.bin -f /opt/apps/etc/lighttpd/lighttpd.conf\$'
pgrep  -f "$PATTERN"
echo pgrep  -f "$PATTERN"

I would keep the single quotes on the assingment to PATTERN, but totally agree you need the dbl-quoting when using with pgrep or echo.

I hope this helps.

edited Feb 20, 2012 at 17:14

answered Feb 20, 2012 at 17:04

shellter

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1 Comment

Jonathan Leffler Over a year ago

The usage message from pgrep shown includes -f without any argument.

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