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I have these lines in file :

postgres 2609 21030 0 12:49 ? 00:00:00 postgres: postgres postgres [local] idle in transaction postgres 2758 21030 0 12:51 ? 00:00:00 postgres: postgres postgres [local] idle in transaction postgres 28811 21030 0 09:26 ? 00:00:00 postgres: postgres postgres [local] idle in transaction postgres 32200 21030 0 11:40 ? 00:00:00 postgres: postgres postgres [local] idle in transaction postgres 32252 21030 0 11:41 ? 00:00:00 postgres: postgres postgres [local] idle in transaction

I need to separate second column values to process them.I have done this code : 

pid=$(cat idle_log.txt | cut -d" " -f2) echo $pid

but it only gave me 28811 32200 32252 in results.as you see there is no trace of 2609 2758 in list,I want to get them too. Also I want count them after extracting pids. I used :

npid=$(grep -o " " <<< $pid | grep -c .)

it returns 2 for results of 28811 32200 32252 I need it return 3 as count of processes. finally I want to process some thing line by line like in a loop with while but output of commands return results at once,and I can't process them in loop format and one by one.

thank you all for help.

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6 Answers 6

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You can use tr to squeeze the spaces and then use cut to take the second space delimited field:

tr -s ' ' <idle_log.txt | cut -d' ' -f2

Or awk:

awk '{ print $2 }' idle_log.txt

Or sed:

sed -r 's/^[^[:blank:]]+[[:blank:]]+([^[:blank:]]+)(.*)/\1/' idle_log.txt

Or grep:

grep -Po '^[^\s]+\s+\K[^\s]+' idle_log.txt

To use/count them later use an array:

pids=( $(tr -s ' ' <idle_log.txt | cut -d' ' -f2) ) num_of_pids="${#pids[@]}" $ printf '%s\n' "${pids[@]}" 2609 2758 28811 32200 32252

Example:

$ tr -s ' ' <file.txt | cut -d' ' -f2 2609 2758 28811 32200 32252 $ awk '{ print $2 }' file.txt 2609 2758 28811 32200 32252 $ sed -r 's/^[^[:blank:]]+[[:blank:]]+([^[:blank:]]+)(.*)/\1/' file.txt 2609 2758 28811 32200 32252 $ grep -Po '^[^\s]+\s+\K[^\s]+' file.txt 2609 2758 28811 32200 32252
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2 Comments

hmmm,nice trick but I still need to get values like one at each time .
thank you for your time I just used the first answer that was more close to my case.
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$ cat data postgres 2609 21030 0 12:49 ? 00:00:00 postgres: postgres postgres [local] idle in transaction postgres 2758 21030 0 12:51 ? 00:00:00 postgres: postgres postgres [local] idle in transaction postgres 28811 21030 0 09:26 ? 00:00:00 postgres: postgres postgres [local] idle in transaction postgres 32200 21030 0 11:40 ? 00:00:00 postgres: postgres postgres [local] idle in transaction postgres 32252 21030 0 11:41 ? 00:00:00 postgres: postgres postgres [local] idle in transaction I need to extract second column from each line, $ awk '{print $2}' data 2609 2758 28811 32200 32252

or you can squeeze multiple spaces into 1 using tr and then use cut like this: 

$ tr -s ' ' < data | cut -d ' ' -f 2 2609 2758 28811 32200 32252

Edit: 

$ tr -s ' ' < data | cut -d ' ' -f 2 | while read -r line || [[ -n "$line" ]]; do > echo "$line" #put your custom processing logic here > done 2609 2758 28811 32200 32252
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Thanks,have you any idea to not output them at once ? I need to read values line by line . . .
I want to calculate elapsed time of Idle in transaction processes and if they passed five minutes I should send mail to its owner to check it.
@Ali_T yes you can write that logic where i have used echo ..
just one thing I want to pass "tr . . . " result to variable as "pid" to get the elapsed time,but while is pipelined with it...any idea ?
@Ali_T if you store in a variable called pid, you will have to use the while loop on that variable pid not in the above format
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grep with Perl regex:

grep -oP '^[\S]+\s+\K[\S]+' file 2609 2758 28811 32200 32252

Or,

grep -o '^\([^[:blank:]]*[[:blank:]]*\)\{2\}' file |grep -o '[0-9]\+' 2609 2758 28811 32200 32252
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cut uses exactly the delimiter you pass it. That means with delimiter ' ', the first line is:

postgres, <empty>, 2609

And the last one is:

postgres, 32252

You can simplify this by running just awk '{print $2}' idle_log.txt

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I'd go for the simplest solution:

pid=$(awk '{print $2}' idle_log.txt) echo $pid

The regex stuff for sed and grep are much less readable in a script while cut and tr may sometimes have unexpected results.

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As has already been pointed out, the reason, you were not getting, the results is that you were not extracting the second column.

Instead, you were using the command cut -d" " -f2 so you were getting the second tablespaced split of each line . You may see that there is an additional tablespace for the two first lines so you should use cut -d" " -f3 but as discussed, this is not the right way to get the second column. Use awk '{print $2}' instead.

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