Linux – “grep” from certain lines to the end of file

command linelinux

I have a text file similar to this:

line 1
line 2A
line 3
line 4A
line 5

I want to "grep" from "line 2A" to the end of file, something like this

cat file.txt|some_grep "line 2A"

Also, I want to "grep" from "line 2A" to the next line that contains "A", something like this

cat file.txt| some_grep "A"

I want this to print out:

line 2A
line 3
line 4A

Which command can help me achieve this?

Best Answer

(expanded from comment)

awk has a capability to select 'ranges' of lines which matches this need perfectly, as described in the the GNU-awk (gawk) manual. (This feature works in other awks but the gawk manual is easy to link.)

awk '/line 2A/,0' prints lines starting with the first one that matches line 2A and continuing until the end of input because 0 is a condition that is never true.

awk '/line 2A/,/A/&&!/line 2A/' starts printing with a line that matches line 2A and stops after a line that matches A but NOT line 2A (and thus cannot be the same line as the starting line). It will start again on a subsequent line 2A and so on; if you want to prevent that there are slightly more complicated ways to do so.

If the stopping lines always have some character other than 2 before the A this can be simplified to awk '/line 2A/,/[^2]A/' which stops after a line that matches any character other than 2, followed by A. You might want a variation of this, e.g. to stop on any-single-digit-A different from 2A, but not other As like WHAT; for that the stopping condition might be ,/line [013-9]A/.

Related Solutions

Linux – How to append text to a specific lines in a file using shell script

With perl, by actually checking if the process is running (Linux only):

perl -ape '$pid = $F[1]; if (-d "/proc/$pid") {s/$/ running/}'

With sed:

sed -i '/\<3696\>/ s/$/ running/' "$file"

With perl:

perl -i -pe 's/$/ running/ if /\b3696\b/' "$file"

perl -i -ape 's/$/ running/ if $F[1] eq "3696"' "$file"

With ed:

ed "$file" <<-EOF
/\<3696\>/ s/$/ running/
wq
EOF

(Here \< \> (sed) and \b \b (perl) mean word boundaries – both examples only match "3696", but not "136960" or such.)

Using grep to remove lines from a file which contain a string from another file

You can do this using grep's -f option (that's lower-case -f, not -F):

% echo -e 'Dog\nFish\nCat\nShoes' > ./file1.txt 
% echo -e '1,shoes,red\n2,apple,black\n3,fog,blue' > ./file2.csv 

# Grab all lines from the CSV that match a pattern from file1:
% grep -if ./file1.txt ./file2.csv
1,shoes,red

# Grab all lines from the CSV that DON'T match a pattern from file1:
% grep -vif ./file1.txt ./file2.csv
2,apple,black
3,fog,blue

Detailed explanation:

grep — self-explanatory
-v — means 'return lines not matching the input pattern'
-i — means 'use case-insensitive matching' (since your first file had capital letters and the CSV didn't)
-f — means 'interpret each line in the specified file (file1.txt) as a pattern to use for matching'

Depending on the results you want and the contents of your files, you may also want to read into the -F and -w options.

If you need to edit the file in-place, i think you can do this with sed's -f option, but sed interprets each line of the file as a command rather than a simple pattern like grep does.

Best Answer

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Linux – How to append text to a specific lines in a file using shell script

Using grep to remove lines from a file which contain a string from another file

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