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Looping through the content of a file in Bash
Often it is a requirement to read each of the line from a file using a bash script. There are various approaches to read the lines form a file. In the below example we have first described how to create a sample file and then run a script reading that sample file.
Create a file to Read
# Open vi Editor vi a_file.txt # Input the below lines Monday Tuesday Wednesday Thursday Friday Saturday Sunday # cat the file cat a_file.txt
Running the above code gives us the following result −
Monday Tuesday Wednesday Thursday Friday Saturday Sunday
Using Do-While
In this approach we use a do-while loop to read a file. We give the file name as an input at the end of the file. First we create a script and give the execute permission to it. Then only it can read the file and show the result.
#!/bin/bash while read LINE do echo "$LINE" done < a_file.txt
Running the above code gives us the following result −
Monday Tuesday Wednesday Thursday Friday Saturday Sunday
Using for and in
In next approach we use a for loop along with the in clause. Here we store the result of cat command (which is each line) in a variable which is part of for loop and echo the variable.
#!/bin/bash file=a_file.txt for i in `cat $file` do echo "$i" done
Running the above code gives us the following result −
Monday Tuesday Wednesday Thursday Friday Saturday Sunday
With only echo
We can also get the content of the file by using only echo. But the result will come out as an array of lines and printed out as one-line output showing combination of all the lines.
echo $( < a_file.txt )
Running the above code gives us the following result:
Monday Tuesday Wednesday Thursday Friday Saturday Sunday
Reading File with Blank Lines
If a file has some lines which are blank then we ca avoid them in the output by using the following code. This uses the IFS (internal Field Separator) is set to empty string so that the blank lines are treated as field separator and avoided in the output. Assuming there are blank lines between 3rd and 4th line, those blank liens will not be printed.
#!/bin/bash while IFS = read -r LINE do echo "$LINE" done < a_file.txt
Running the above code gives us the following result −
Monday Tuesday Wednesday Thursday Friday Saturday Sunday
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