shell errors running php exec

Question

I have a PHP script that executes a shell command to find the common items between two files given. This is the beginning of my PHP script:

$E7Bonded_File = "/opt/IBM/custom/NAC_Dslam/junk/PortParameter_E7_Bonded_cust_stats.csv";
$E7Single_File = "/opt/IBM/custom/NAC_Dslam/junk/PortParameter_E7_Single_cust_stats.csv";
$E7Common_File = "/opt/IBM/custom/NAC_Dslam/junk/Common_tn_SingleBonded_E7_cust_stats.csv";
//only do this once, with old single/bonded filenames. This will be a list to add to the existing Common file.
exec ("comm -12 <(cut -d ',' -f2 $E7Single_File| sort) <(cut -d ',' -f2 $E7Bonded_File| sort)", $outputCommon);

I see this error message when I run the script:

sh: -c: line 0: syntax error near unexpected token `('
sh: -c: line 0: `comm -12 <(cut -d ',' -f2 /opt/IBM/custom/NAC_Dslam/junk/PortParameter_E7_Single_cust_stats.csv| sort) <(cut -d ',' -f2 /opt/IBM/custom/NAC_Dslam/junk/PortParameter_E7_Bonded_cust_stats.csv| sort)'

I checked, and the parentheses look ok for my exec() line.

When I run the shell command at the command line it returns a listing of numbers like I expect:

 comm -12 <(cut -d ',' -f2 junk/PortParameter_E7_Single_cust_stats.csv| sort) <(cut -d ',' -f2 junk/PortParameter_E7_Bonded_cust_stats.csv| sort)

I looked online and I seem to be using exec() correctly. I want the numbers returned to be stored as an array, $outputCommon.

Any ideas about this error message?

*********Update on answer***************

My solution wound up being a combination of both mario and miken32/my co-worker

Adding #!/bin/bash at the top of my php script, and
Adding /bin/bash -c as follows:

exec("/bin/bash -c /opt/IBM/custom/NAC_Dslam/Common_list.sh", $outputShell);
After I moved the comm part to a shell script:

Common_list.sh:

#!/bin/bash
 comm -12 <(cut -d ',' -f2 /opt/IBM/custom/NAC_Dslam/junk/PortParameter_E7_Single_cust_stats.csv| sort) <(cut -d ',' -f2 /opt/IBM/custom/NAC_Dslam/junk/PortParameter_E7_Bonded_cust_stats.csv| sort)

Which shell are you using for testing, and which one is linked as /bin/sh? dash does not support expression pipes AFAIK. — mario
– mario, Commented Jul 27, 2018 at 17:38
I did "which sh" at the command line and it returned /bin/sh. I added this line to my script, exec("which sh",$throwaway); var_dump($throwaway); and it returned /bin/sh as well. I've used pipes in commands I execute in php exec before. — Michele
– Michele, Commented Jul 27, 2018 at 17:49
Is the issue specific to comm? Or to Linux? Also check the description of the "shell" tag. That said, your question is off-topic because it really lacks a minimal reproducible example. — Ulrich Eckhardt
– Ulrich Eckhardt, Commented Jul 27, 2018 at 19:39

mario · Accepted Answer · 2018-07-27 19:43:09Z

3

This error typically comes up for non-bash shells, which don't support <() expression pipes.

On Ubuntu/Debian servers the default /bin/sh is typically dash.

Check for symlinked binaries:

me@snip:~$ ls -l /bin/sh
lrwxrwxrwx 1 root root 4 Jul 16  2017 /bin/sh -> dash

Or as @theotherguy mentioned, bash runs as restricted_shell when started as sh.
See $_ENV[SHELL] on what Apache/PHP use as default. Change environment vars.
Either adapt that, or wrap the shell_exec cmdline with /bin/bash -c '…'.

edited Jul 27, 2018 at 19:43

answered Jul 27, 2018 at 18:17

mario

146k20 gold badges243 silver badges293 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

Michele Over a year ago

Did you mean to type "dash" above there?

Michele Over a year ago

mario-It's not clear what I need to do with what you're saying in your answer.

that other guy Over a year ago

Even when sh is bash, it'll run in a compatibility more where process substitution is not available

mario Over a year ago

@thatotherguy So it'll only work for real login or interactive shells? // Then -l or +o restricted might be necessary.

that other guy Over a year ago

No, it's fine in non-interactive shells. It just requires that bash is invoked as bash, such as with bash -c

|

miken32 · Accepted Answer · 2018-07-27 20:58:48Z

2

Probably the easiest solution would be to make this into an executable script on the server:

#!/bin/bash
if [[ ! -r "$1" ]] || [[ ! -r "$2" ]]; then
    printf "File not found\n" >&2
    exit 1
fi

comm -12 <(cut -d ',' -f2 "$1"| sort) <(cut -d ',' -f2 "$2"| sort)

And then call that from PHP:

$E7Bonded_File = escapeshellarg("/opt/IBM/custom/NAC_Dslam/junk/PortParameter_E7_Bonded_cust_stats.csv");
$E7Single_File = escapeshellarg("/opt/IBM/custom/NAC_Dslam/junk/PortParameter_E7_Single_cust_stats.csv");

//only do this once, with old single/bonded filenames. This will be a list to add to the existing Common file.
exec ("/usr/local/bin/your_script.sh $E7Single_File $E7Bonded_File", $outputCommon);

Always escape your shell arguments with escapeshellarg() even if you think they're safe.

answered Jul 27, 2018 at 20:58

miken32

42.5k16 gold badges127 silver badges177 bronze badges

5 Comments

Michele Over a year ago

I tried this, and running the shell script with the command has the same complaint. That's strange, since the command runs at the command line.

miken32 Over a year ago

I find that hard to believe since the shebang tells it to run under bash. Did you mark the script executable?

Michele Over a year ago

Yes, I made it chmod 777. I got something to work. I moved the comm part to the shell script like you have, with bin bash at the top, and I run the shell script like this from my php script: exec("/bin/bash -c /opt/IBM/custom/NAC_Dslam/Common_list.sh", $outputShell); I also have the #!/bin/bash at the top of my php script.

Michele Over a year ago

BTW, the shell script ran from the command line, just not from the php script until I made those changes.

Michele Over a year ago

It was adding /bin/bash/ -c in front of my exec in the php script that seemed to help

Martin Zeitler · Accepted Answer · 2018-07-30 19:20:43Z

0

when checking the script with a linter, it complains that:

comm -12 <(cut -d ',' -f2 junk/PortParameter_E7_Single_cust_stats.csv| sort) <(cut -d ',' -f2 junk/PortParameter_E7_Bonded_cust_stats.csv| sort)
     ^-- SC2039: In POSIX sh, process substitution is undefined.

this happens when I define shebang #!/bin/sh, while #!/bin/bash does not complain... therefore the answer might be, to run the script with /usr/bin/bash. escapeshellarg() is indeed useful.

...

try shell_exec(), simply because exec() should not invoke any shell. the one returns the output as string and the other can return an array. alternatively, you can explicitly invoke bash with exec():

exec('/bin/bash -c "  command  "', $stdOut);

edited Jul 30, 2018 at 19:20

answered Jul 28, 2018 at 4:42

Martin Zeitler

79.6k20 gold badges169 silver badges243 bronze badges

1 Comment

Michele Over a year ago

Are you saying to run the comm command as a shell script using #!/usr/bin/bash. I'm trying that right now, and it has the same error, when executed from my php script.

morphles · Accepted Answer · 2022-04-22 13:31:13Z

0

So in case anyone else still needs to get substitution working in command execution in PHP, there is super dumb simple thing to do:

$a = 'Hello substitution';
var_dump(shell_exec("bash -c 'cat <(echo $a)'"));

Results in:

string(19) "Hello substitution
"

Which is expected/desired.

answered Apr 22, 2022 at 13:31

morphles

2,5031 gold badge24 silver badges28 bronze badges

Collectives™ on Stack Overflow

shell errors running php exec

4 Answers 4

6 Comments

5 Comments

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

6 Comments

5 Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related