CODEWITHSUNDEEP
bash
Reinhold Kainhofer
Reinhold Kainhofer

Reputation: 340

Adding a header line to output of scripts in Bash (only if script generates output)

I have a Bash script that calls several other scripts (syncing user lists / detecting inconsistencies). For each script that produces an output, I'd like to add a header before the actual output, but for scripts without any output, I don't want anything printed.

Currently, I simply print out the header line in any case:

#!/bin/bash
for scrpt in test1.sh test2.sh; do
    echo "Script $scrpt printed out:"
    ./${scrpt}
done

However, what I want is the "Script $script printed out:" to appear only when ./${scrpt} really produces some output.

I could store the output in a variable and check that:

#!/bin/bash
for scrpt in test1.sh test2.sh; do
  ctnt=`./${scrpt}`
  if [ -n "$ctnt" ]; then
    echo -e "Script returned (with temporary variable): \n$ctnt"
  fi
done

However, my scripts run quite some time, so I'd like the ouput to appear as soon as it is created. And before the first output is printed, the header should appear. So while the above generates the output that I need, is not a good solution for me.

What I have in mind is something that can be called like:

#!/bin/bash
for scrpt in test1.sh test2.sh; do
  ./${scrpt} | print-text-before-first-output "Script $scrpt printed:"
done

Is there such a utility available?

Upvotes: 1

Views: 1355

Answers (1)

Cyrus
Cyrus

Reputation: 88731

With GNU sed: replace

./${scrpt}

with

./${scrpt} | sed '1s/^/Header\n&/'

Upvotes: 2

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