CODEWITHSUNDEEP
perlawksedpattern-matching
Gabriel
Gabriel

Reputation: 3097

How do I replace a substring by the output of a shell command with sed, awk or such?

I'd like to use sed or any command line tool to replace parts of lines by the output of shell commands. For example:

sed seems best fitted because it allows to match patterns and reformat other things too, like moving bits of matches around, but is not mandatory.

Here is a simplified example:

echo "timestamp = 1234567890" | sed "s/timestamp = \(.*\)/timestamp = $(date -u --d @\1 "+%Y-%m-%d %T")/g"

Of course, the $(...) thing does not work. As far as I understand, that's for environment variables.

So what would the proper syntax be? Is sed recommended in this case ? I've spent several hours searching... Is sed even capable of this ? Are there other tools better suited?

Edit

I need...

Upvotes: 5

Views: 2654

Answers (2)

fedorqui
fedorqui

Reputation: 290075

To run an external command in sed you need to use e. See an example:

$ echo "timestamp = 1234567890" | sed "s#timestamp = \(.*\)#date -u --d @\1 "\+\%Y"#e"
2009

With the full format:

$ sed "s#timestamp = \(.*\)#echo timestamp; date -u --d @\1 '\+\%Y-\%m-\%d \%T'#e" <<< "timestamp = 1234567890"
timestamp
2009-02-13 23:31:30

This catches the timestamp and converts it into +%Y format.

From man sed:

e

This command allows one to pipe input from a shell command into pattern space. If a substitution was made, the command that is found in pattern space is executed and pattern space is replaced with its output. A trailing newline is suppressed; results are undefined if the command to be executed contains a nul character. This is a GNU sed extension.

However, you see it is a bit "ugly". Depending on what you want to do, you'd better use a regular while loop to fetch the values and then use date normally. For example, if the file is like:

timestamp = 1234567890

Then you can say:

while IFS="=" read -r a b
do
  echo "$b"
done < file

this will make you have $b as the timestamp and then you can perform a date ....

Upvotes: 4

glenn jackman
glenn jackman

Reputation: 247012

As commented, use a language with built-in time functions. For example:

$ echo "timestamp = 1234567890" | gawk '{$3 = strftime("%F %T", $3)} 1'
timestamp = 2009-02-13 18:31:30

$ echo "timestamp = 1234567890" | perl -MTime::Piece -pe 's/(\d+)/ localtime($1)->strftime("%F %T") /e'
timestamp = 2009-02-13 18:31:30

Upvotes: 2

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