CODEWITHSUNDEEP
bashshellwhile-loopif-statement
bikerben
bikerben

Reputation: 483

While Do Statement with blank/empty grep return?

This is the code for my foobar.sh:

!#/bin/bash
while [ 1 ]
do
    pid=`ps -ef | grep "mylittleprogram" | grep -v grep | awk ' {print $2}'`
    echo $pid
    if [ "$pid"="" ]
    then
            echo "Process has ended lets get this show on the road..."
            exit
    else
            echo "Process has not ended yet"
    fi
    sleep 6
done

I'm basically running a infinate loop which will execute command X once a monitored process has ended but I end up getting the following message as my script loops:

./foobar.sh: line 7: [: missing `]'
Process has not ended yet

Is there a way of making the script accept that zero feed back will trigger my 'Then' statement and execute command X since it is not liking the current method.

Upvotes: 7

Views: 38984

Answers (4)

A.H.
A.H.

Reputation: 66243

Instead of 

if [ "$pid"="" ]

please try

if [ "$pid" = "" ]

The whitespace is around = is important.

You can also try

if [ -z "$pid" ]

Upvotes: 15

JRFerguson
JRFerguson

Reputation: 7516

Instead of the nebulous matching provided by:

pid=`ps -ef | grep "mylittleprogram" | grep -v grep | awk ' {print $2}'`

...and the archaic backtick syntax, consider this which matches the process basename exactly and produces an output format of your choice (here, the process pid if it exists):

pid=$(ps -C mylittleprogram -opid=)

Then, as noted, simply test for an empty value:

[ -z "${pid" ] && echo "no process" || echo "I live as $pid"

The equal sign following the output element name suppresses the heading that you would normally get. Manpages are your friend.

Upvotes: 0

sehe
sehe

Reputation: 392911

I'd do 

while pgrep -fl "mylittleprogram"; do sleep 6; done
exit # process has ended

(pgrep is in package psmisc IIRC)

I've just tested it. You could redirect the output of pgrep to /dev/null if you wanted the waiting to be silent. Add some more spice to make things uninterruptible:

{
     trap "" INT
     while pgrep -fl "mylittleprogram" >/dev/null
     do 
         sleep 6
     done
     true
} && exit

Upvotes: 3

chx
chx

Reputation: 11760

The zero test is if [ -z "$pid" ]

Upvotes: 2

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