[bash] How to add to the end of lines containing a pattern with sed or awk?

Here is example file:

somestuff...
all: thing otherthing
some other stuff

What I want to do is to add to the line that starts with all: like this:

somestuff...
all: thing otherthing anotherthing
some other stuff

Solution with awk:

awk '{if ($1 ~ /^all/) print $0, "anotherthing"; else print $0}' file

Simply: if the row starts with all print the row plus "anotherthing", else print just the row.

In bash:

while read -r line ; do
    [[ $line == all:* ]] && line+=" anotherthing"
    echo "$line"
done < filename

Here is another simple solution using sed.

$ sed -i 's/all.*/& anotherthing/g' filename.txt

Explanation:

all.* means all lines started with 'all'.

& represent the match (ie the complete line that starts with 'all')

then sed replace the former with the later and appends the ' anotherthing' word

This should work for you

sed -e 's_^all: .*_& anotherthing_'

Using s command (substitute) you can search for a line which satisfies a regular expression. In the command above, & stands for the matched string.

You can append the text to $0 in awk if it matches the condition:

awk '/^all:/ {$0=$0" anotherthing"} 1' file

Explanation

• /patt/ {...} if the line matches the pattern given by patt, then perform the actions described within {}.
• In this case: /^all:/ {$0=$0" anotherthing"} if the line starts (represented by ^) with all:, then append anotherthing to the line.
• 1 as a true condition, triggers the default action of awk: print the current line (print $0). This will happen always, so it will either print the original line or the modified one.

Test

For your given input it returns:

somestuff...
all: thing otherthing anotherthing
some other stuff

Note you could also provide the text to append in a variable:

$ awk -v mytext=" EXTRA TEXT" '/^all:/ {$0=$0mytext} 1' file
somestuff...
all: thing otherthing EXTRA TEXT
some other stuff