How to convert shell script variable from string to an integer

Question

My script has a line that measures the number of instances of a process being run

procs=$(pgrep -f luminati | wc -l);

However, even though the content of $procs is a numeral, the shell script is not storing $procs as an integer. It is being stored as a string.

Therefore I cannot run conditionals like

if $procs > 3

Is there any way to convert this variable to integer type?

PS: shellcheck automatically detects this and other common problems. — that other guy
– that other guy, Commented Apr 2, 2018 at 16:34
Everything in shell is a string. You need to use the correct commands and operators that can treat strings as numbers. — chepner
– chepner, Commented Apr 2, 2018 at 17:27

Robert Seaman · Accepted Answer · 2018-04-02 17:47:19Z

2

In bash > is truncate which writes to a file. You probably have a file called 3 now. You should use the comparitor -gt:

if [[ "$procs" -gt 3 ]]; then
    ...
fi

Also, you don't have separate types for integers and strings.

Edit: As @chepner explained, for POSIX compatibility you should use single brackets:

if [ "$procs" -gt 3 ];

edited Apr 2, 2018 at 17:47

answered Apr 2, 2018 at 16:19

Robert Seaman

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4 Comments

hvs Over a year ago

LOL, indeed I had a file called 3 by using the > sign which I knew about but did not think in this context. But your solution is bang on. Thanks.

Diego Torres Milano Over a year ago

'>' is not truncate inside [[ ]], it's ascii comparison

Robert Seaman Over a year ago

@DiegoTorresMilano is right, > doesn't truncate inside [[ ]], however it does inside [ ]! It's always safer to use -gt in my opinion.

chepner Over a year ago

The existence of [[ strongly implies your shell also has ((...)). Use if [ "$procs" -gt 3 ]; for POSIX compatibility or if (( procs > 3 )); for readability.

Diego Torres Milano · Accepted Answer · 2018-04-02 16:21:24Z

2

Should be

if [[ "$procs" -gt 3 ]]
then
 ...
fi

edited Apr 2, 2018 at 16:21

answered Apr 2, 2018 at 16:16

Diego Torres Milano

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1 Comment

Robert Seaman Over a year ago

You mean to use -gt rather than >?

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