Bash单行嵌套for循环将比较变量作为命令

Question

I believe my error is in do if ($i -gt 100) area but I havent been able to figure it out.

My input is:

for i in `ps | cut -d ' ' -f1`; do if ($i -gt 100); then echo $i; fi; done

My output is this where the process IDs have been taken as commands.

bash: 13968: command not found
bash: 21732: command not found
bash: 21733: command not found
bash: 21734: command not found

How can I fix this and what is the relevant man page that I should read up on? Thank you.

Answer 1

if ($i -gt 100)

should be changed to

if [ $i -gt 100 ]

Note that there is a space before and after [] , this is neccessary, otherwise you will get a syntax error (its because [ is a link to test in /usr/bin ).

The relevant manapge would be man test , as [ is test .

Also, but this has nothing to do with the question, I recommend switchting from

`command`

to

$(command)

in bash.

Answer 2

It's not clear what your script is trying to do (the posted answers produce no output on my system) but if you want to print all PIDs that are greater than 100, here's how you'd do that:

$ ps | awk '$1 > 100{print $1}'
PID
314024
217880
230804
217084
263048
260788
218016
313464
201556
200732

Answer 3

只需在括号和表达式之前和之后添加空格

for i in `ps | cut -d ' ' -f1`; do if [ $i -gt 100 ]; then echo $i; fi; done