How to read a file line by line in a bash script?
Jun 12, 2025 am 10:25 AM
The most common way to read file contents line by line in a Bash script is to use a while read loop. 1. Use the while read -r line structure to ensure that lines containing special characters are correctly processed; 2. Use the file content as input by redirecting
The most common method to read file contents line by line in a Bash script is to use a while read loop. This method is simple and effective and is suitable for processing every line of data in a text file.
Read each line of the file using while read
This is the most standard and common practice. The basic structure is as follows:
while read -r line; do
echo "$line"
done < filename.txt- The
-rparameter is important, it prevents backslash escape behavior and avoids accidental truncation or modification of content. -
< filename.txtmeans standard input to redirect the file to loop. -
lineis a variable name, you can change it to another name, such asmy_lineorcontent.
For example, suppose you have a file named names.txt , with a name per line:
Alice Bob Charlie
You can print out each name using the script above.
Process lines containing spaces or special characters
Sometimes the contents of the file may contain special characters such as spaces, Tabs or quotes. At this time, the basic method above is still applicable, provided that -r is added:
while read -r line; do
echo "Processing: $line"
done < data.txt If you missed -r , Bash might merge it into helloworld when you encounter something like hello\world , which is not the result you want.
Dynamically pass file names in scripts
If you want the script to support passing in different file names, you can use it in combination with command line parameters:
#!/bin/bash
filename="$1"
while read -r line; do
echo "$line"
done < "$filename"Operation mode:
./read_file.sh myfile.txt
This allows you to flexibly process different files. Note that you want to check whether the file exists or the script may fail silently.
If you want to add a bit of fault tolerance, you can add a judgment at the beginning:
if [ ! -f "$filename" ]; then
echo "The file does not exist"
exit 1
fiNotes and FAQs
- Don't omit
-rinread: unless you really need backslash connection behavior. - Avoid
cat file | while read ...reading files : Although this writing method works, it can also work in a subshell, which may cause variables to not be retained. - Line breaks at the end of the line do not affect : even if there is no line break at the end of a certain line,
readcan be handled normally. - A blank line will be skipped : By default, a blank line will not enter the loop body. If you want to keep blank lines, you can add
IFS=:
while IFS= read -r line; do
echo "Line: $line"
done < file.txtBasically that's it. Mastering this structure will be easy for you to write automated scripts or log analysis tools.
The above is the detailed content of How to read a file line by line in a bash script?. For more information, please follow other related articles on the PHP Chinese website!
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