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BASH - Files - Read a file - Read fields from a file

To read fields within each line of the file, additional variables may be used with the read:

For instance, if an input file has 3 columns separated by white space (space or tab characters only).

while read -r first_name last_name phone; do
  # Only print the last name (second column).
  printf '%s\n' "$last_name"
done < "$file"

If the field delimiters are not whitespace, set the IFS (internal field separator):

# Extract the username and its shell from /etc/passwd:
while IFS=: read -r user pass uid gid gecos home shell; do
  printf '%s: %s\n' "$user" "$shell"
done < /etc/passwd

NOTE: IFS is set to :.

For tab-delimited files, use IFS=$'\t' though beware that multiple tab characters in the input will be considered as one delimiter (and the IFS=$'\t\t' workaround will not work in Bash).

You do not necessarily need to know how many fields each line of input contains.

If you supply more variables than there are fields, the extra variables will be empty.
If you supply fewer, the last variable gets “all the rest” of the fields after the preceding ones are satisfied.

For example:

read -r first last junk <<< 'Bob Smith 123 Main Street Elk Grove Iowa 123-555-6789'

first: will contain “Bob”
last: will contain “Smith”.
junk: holds everything else.

The throwaway variable _ can be used as a “junk variable” to ignore fields.

It (or indeed any variable) can also be used more than once in a single read command, if we don't care what goes into it:

read -r _ _ first middle last _ <<< "$record"

We skip the first two fields, then read the next three.
The final _ can absorb any number of fields.
- It does not need to be repeated there.

This usage of _ is only guaranteed to work in Bash.

Many other shells use _ for other purposes that will at best cause this to not have the desired effect, and can break the script entirely.
It is better to choose a unique variable that isn't used elsewhere in the script, even though _ is a common Bash convention.