Parsing list in bash

Question

I have a text file which looks like this:

... unique_trigger = item1 item2 item3 ... itemN unique_end_trigger ...

Is there a quick (maybe on-liner if possible) bash script I could use to parse the file and pipe item1 item2 item3... into another command? The number of items is not determined. I looked at other bash scripts to read variables out of a file but they either source it, parse each item manually (predetermined list length) or assign a environment variable to each item based on its name (which is not my case). I am looking for something like this:

parse_command file.txt | other_command

you'll increase the chances of receiving a usable answer if you provide a sample of the actual data; does item contain white space or embedded linefeeds? what do the lines before/after the unique_trigger section look like; do all item entries have a leading = or just the first one? are there any lines in the unique_trigger section that should not be printed? — markp-fuso
– markp-fuso, Commented May 6, 2022 at 16:11
Why not use an existing format like JSON and existing tools like jq? — chepner
– chepner, Commented May 6, 2022 at 16:38
@chepner because I am stuck with this format which is required by some other tool. — fgoudra
– fgoudra, Commented May 6, 2022 at 16:53
@markp-fuso items don't have spaces. I'm not sure what are embedded linefeeds? — fgoudra
– fgoudra, Commented May 6, 2022 at 16:53

glenn jackman · Accepted Answer · 2022-05-06 17:41:38Z

2

perl:

perl -0777 -pE 's/.*unique_trigger\s*=\s*(.*)unique_end_trigger.*/$1/s; s/^\s+//gm' file.txt

item1 item2 item3 ... itemN

answered May 6, 2022 at 17:41

glenn jackman

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seeker · Accepted Answer · 2022-05-06 16:13:36Z

1

One-liner

cat file.txt | tr -s "[:space:]" " " | \ sed -En "s/(.*)(unique_trigger = )(.*)(unique_end_trigger)/\3/p" | \ other_command

answered May 6, 2022 at 16:13

seeker

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1 Comment

glenn jackman Over a year ago

Nice ides with squeezing the whitespace. An alternate take: tr -s '[:space:]' '\n' < file.txt | sed -En '/unique_trigger/,/unique_end_trigger/ {/^=|unique_(end_)?trigger$/!p;}'

ufopilot · Accepted Answer · 2022-05-06 19:24:27Z

 awk '/unique_end_trigger/&&--f||f||/unique_trigger/&&f++ {printf $1 " "}' <(sed 's/unique_trigger =/ & \n /' input_file) item1 item2 item3 ... itemN

Ljm Dullaart · Accepted Answer · 2022-05-06 16:03:51Z

Not quite a one-liner, but it should do the trick as long as your triggers don't contain spaces.

flag=0 while read tr eq it ; do if [ "$tr" = "unique_trigger" ] ; then echo "$it" flag=1 elif [ $flag = 1 ] ; then if [ "$tr" = "unique_end_trigger" ] ; then flag=0 else echo "$tr" fi fi done

Nic3500 · Accepted Answer · 2022-05-06 17:00:39Z

Two solutions, using the same concept. When the start trigger is found, add the item (3rd item in the line) to a string. Until the end trigger is found, the item is the only work in the line, so add it to the string. Output the string at the end.

Bash parsing

#!/bin/bash file="file.txt" start_trigger="unique_trigger" end_trigger="unique_end_trigger" items='' between_trigger="no" while IFS= read -r line; do #echo "-----$line-----" # Start trigger lines if [[ "$line" =~ "$start_trigger =" ]] then items="$items $(echo "$line" | awk '{print $3}')" between_trigger="yes" continue fi # End trigger lines if [[ "$line" =~ "$end_trigger" ]] then between_trigger="no" continue fi # Lines between start and end trigger if [[ "$between_trigger" == "yes" ]] then items="$items $line" continue fi done < "$file" echo ">>$items<<"

Using it: script.bash | xargs echo

Replace echo by any command.

Awk version

BEGIN { output = "" between = "no" } /unique_end_trigger/ { between = "no"; } /.*/ { if (between == "yes") output = output " " $1 } /unique_trigger/ { between = "yes"; output = output " " $3; } END { print output }

Using it: awk -f script.awk file.txt | xargs echo

Replace echo with whatever command you want.

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