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Prefix to each output of a command on runtime

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Original source (superuser.com)
Tags: bash shell-scripting
Clipped on: 2016-04-03

I am trying to make a modular script. I have several scripts/commands which are called from a single script.
I want to prefix the output of each separate command.

Examle:

My files are allcommands.sh / command1.sh / command2.sh

command1.sh outputs
file exists
file moved

command2.sh outputs
file copied
file emptied

allcommands.sh runs the scripts command1.sh and command2.sh

I want to prefix each output of these two scripts like this:
[command1] file exists
[command1] file moved
[command2] file copied
[command2] file emptied

asked Jul 23 '13 at 10:58
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Ivan Dokov
1315
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Try running each command piping it through sed "s/\^/command1 /" – j_kubik Jul 23 '13 at 11:08
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Give me please an example with the information that I give. I don't really understand the sed functionality. I'm sorry. – Ivan Dokov Jul 23 '13 at 11:18
up vote 10 down vote accepted

I assume that what you are doing in your allcommands.sh is:

command1.sh
command2.sh

Just relace it with

command1.sh | sed "s/^/[command1] /"
command2.sh | sed "s/^/[command2] /"
answered Jul 23 '13 at 11:29
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j_kubik
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This works perfectly for my case. Thanks! – Ivan Dokov Jul 23 '13 at 11:38
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+1 for simplicity. – Daniel Andersson Jul 23 '13 at 11:41

A minimal example of allcommands.sh:

#!/bin/bash
for i in command{1,2}.sh; do
    ./"$i" | sed 's/^/['"${i%.sh}"'] /'
done

With command1.sh and command2.sh executable and in the same directory just echoing the wanted strings, this gives the shell output:

$ ./command1.sh 
file exists
file moved
$ ./command2.sh 
file copied
file emptied
$ ./allcommands.sh 
[command1] file exists
[command1] file moved
[command2] file copied
[command2] file emptied

Quick sed breakdown

sed 's/^/['"${i%.sh}"'] /'
  • s/ enters "regexp pattern match and replace" mode
  • ^/ means "match the beginning of every line"
  • ${i%.sh} happens in the shell context and means "$i, but strip the suffix .sh"
  • ['"${i%.sh}"'] / at first prints a [, then exits the quoted context to grab the $i variable from the shell, then re-enters to finish with the ] and a space.
answered Jul 23 '13 at 11:28
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Daniel Andersson
14.9k12540
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Thanks for the clarifications. Your answer was helpful indeed, but @j_kubik's example was just the one I need. – Ivan Dokov Jul 23 '13 at 11:39

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