Using Bash Script to Find Line Number of String in File

Question

How can I use a bash script to find the line number where a string occurs?

For example if a file looked like this,

Hello I am Isaiah
This is a line of text.
This is another line of text.

and I ran the script to look for the string "line" it would output the number 2, as it is the first occurance.

Solution 1

Given that your example only prints the line number of the first occurrence of the string, perhaps you are looking for:

awk '/line/{ print NR; exit }' input-file

If you actually want all occurrences (eg, if the desired output of your example is actually "2\n3\n"), omit the exit.

Solution 2

I like Siddhartha's comment on the OP. Why he didn't post it as an answer escapes me.

I usually just want the line number of the first line that shows what I'm looking for.

lineNum="$(grep -n "needle" haystack.txt | head -n 1 | cut -d: -f1)"

Explained: after the grep, grab just the first line (num:line), cut by the colon delimiter and grab the first field

Solution 3

For an exact match, I use

grep -wn <your exact match word> inputfile | cut -d: -f1

Explained: -n print the line number -w to only return the line with exact match

Comments

[Siddhartha]

You could just do grep -n "line" file.txt and it'll give you the line numbers.

[Siddhartha]

Also grep --color=always -n "line" file.txt will highlight in red the occurences of the word 'line'

[Farhan Ahmed Wasim]

I have tried using the above command, with the string 'line' stored in a variable. I had read somewhere, that when we are trying to use an external variable within an awk command, it is good to first assign the external variable to a local awk variable. As such I tried the following command: awk -v var="$external_variable" '/external_variable/{ print NR; exit }' input-file but the command didn't return the line number. Can you tell me what I am doing wrong?

[William Pursell]

You need to use match rather than //. For example: awk 'match($0,v){print NR; exit}' v=$external_variable input-file should work.

[i spin and then i lock]

head -n 1 can be replaced with -m 1 flag in grep