Parsing command output in bash to variables

Question

I have a number of bash scripts, each doing its own thing merrily. Do note that while I program in other languages, I only use Bash to automate things, and am not very good at it.

I'm now trying to combine a number of them to create "meta" scripts, if you will, which use other scripts as steps. The problem is that I need to parse the output of each step to be able to pass a part of it as params to the next step.

An example:

stepA.sh

[...does stuff here...]
echo "Task complete successfuly"
echo "Files available at: $d1/$1"
echo "Logs available at: $d2/$1"

both the above are paths, such as /var/www/thisisatest and /var/log/thisisatest (note that files always start with /var/www and logs always start with /var/log ). I'm only interested in the files path.

steB.sh

[...does stuff here...]
echo "Creation of $d1 complete."
echo "Access with username $usr and password $pass"

all variables here are simple strings, that may contain special characters (no spaces)

What I'm trying to build is a script that runs stepA.sh, then stepB.sh and uses the output of each to do its own stuff. What I'm currently doing (both above scripts are symlinked to /usr/local/bin without the .sh part and made executable):

 #!/bin/bash

 stepA $1 | while read -r line; do
 # Create the container, and grab the file location
 # then pass it to then next pipe
   if [[ "$line" == *:* ]]
   then
     POS=`expr index "$line" "/"`
     PTH="/${line:$POS}"
     if [[ "$PTH" == *www* ]]
     then
       #OK, have what I need here, now what?
       echo $PTH;
     fi
   fi
done 

# Somehow get $PTH here

stepB $1 | while read -r line; do
 ...
done

#somehow have the required strings here

I'm stuck in passing the PTH to the next step. I understand this is because piping runs it in a subshell, however all examples I've seen refer to to files and not commands, and I could not make this to work. I tried piping the echo to a "next step" such as

stepA | while ...
    echo $PTH
done | while ...
 #Got my var here, but cannot run stuff
done

How can I run stepA and have the PTH variable available for later? Is there a "better way" to extract the path I need from the output than nested ifs ?

Thanks in advance!

+1 for well formatted question and much apparent work on your problem. .... but... its hard to understand how we can help. Some actual output of your current process might help, plus some expected output, both as the final output, and what you see in the intermediate outputs of stepA and stepB might help. Also I'm not clear if you just want the value of PTH to pass between stepA->B OR do you want step B to have a $PTH variable (with a value) that it has "inherited" from the stepA. Good luck! — shellter
– shellter, Commented Mar 9, 2013 at 14:06

Gordon Davisson · Accepted Answer · 2013-03-09 16:39:17Z

4

Since you're using bash explicitly (in the shebang line), you can use its process substitution feature instead of a pipe:

while read -r line; do
    if [[ "$line" == *:* ]]
        .....
    fi
done < <(stepA $1)

Alternately, you could capture the command's output to a string variable, and then parse that:

output="$(stepA $1)"
tmp="${output#*$'\nFiles available at: '}" # output with everything before the filepath trimmed
filepath="${tmp%%$'\n'*}" # trim the first newline and everything after it from $tmp
tmp="${output#*$'\nLogs available at: '}"
logpath="${tmp%%$'\n'*}"

edited Mar 9, 2013 at 16:39

answered Mar 9, 2013 at 13:05

Gordon Davisson

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1 Comment

Nick Andriopoulos Over a year ago

this will do nicely, thanks. the second method actually looks "cleaner".

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