CODEWITHSUNDEEP
linuxbashsedscripting
Wyatt_LandWalker
Wyatt_LandWalker

Reputation: 309

Edit a line and create it if it's not found

Basically i got a "database", and a function in my script to install applications. So this function down here searches for:

is-program-installed=

and happens "1" when "program" installation finishes:

is-program-installed= 1

but what happens if the line is not found and i want that function to write one?

function dbmarktrue () {

table=${1?Usage: dbmarktrue $editdbtable}

sed -e "/^is-$table-installed=/ s/.$/1/" -i database.txt
}

Upvotes: 1

Views: 40

Answers (1)

fedorqui
fedorqui

Reputation: 290355

I would go through the file and perform the replacement; if it happens, set a flag. And finally, after the whole file was processed, print it if such flag was not set:

awk -v replace="is-program-installed=1" '
       $0 == "is-program-installed=" {$0=replace; seen=1}1;
       END {if (!seen) print replace}' a

Test

It was not present:

$ cat a
hello
$ awk -v replace="is-program-installed=1" '$0 == "is-program-installed=" {$0=replace; seen=1}1; END {if (!seen) print replace}' a
hello
is-program-installed=1

It was present:

$ cat a
hello
is-program-installed=
$ awk -v replace="is-program-installed=1" '$0 == "is-program-installed=" {$0=replace; seen=1}1; END {if (!seen) print replace}' a
hello
is-program-installed=1

As usual, awk to replace the original file you can redirect the output to a temporary file and then move to the original:

awk '...' file > tmp_file && mv tmp_file file

By using && we make sure the mv command is not executed if the awk exits with an error.

Upvotes: 4

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