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Learn how to use the -F option in awk to customize the field separator when processing structured text. By default, awk splits records on whitespace, but -F lets you define any character or regular expression as the delimiter. 
usage: awk [-F fs] [-v var=value] [-f progfile | 'prog'] [file ...]

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1. Default Field Splitting

By default, awk treats any whitespace as the field separator: 
$ df -h

Filesystem      Size  Used Avail Use% Mounted on
udev            1.8G     0  1.8G   0% /dev
tmpfs           366M  9.7M  356M   3% /run
...
When your data uses a different delimiter—such as commas, colons, or pipes—you must override this behavior.

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2. Changing the Field Separator with -F

To use a colon (:) as the separator: 
$ awk -F ":" '{ print $1 }' sizeV1.txt

Filesystem
udev
tmpfs
/dev/sda1
...
Print the second field: 
$ awk -F ":" '{ print $2 }' sizeV1.txt

Size
1.8G
366M
...
Combine fields 1 and 5: 
$ awk -F ":" '{ print $1, $5 }' sizeV1.txt

Filesystem Use%
udev 0%
tmpfs 3%
...
You can also pipe data into awk: 
$ cat sizeV1.txt | awk -F ":" '{ print $2 }'

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3. Why Quote or Escape the Separator

Certain characters (for example, |, &, *, <, >) have special meanings to the shell.
Always quote or escape the field separator to prevent shell interpretation.Incorrect:
awk -F | '{ print $1 }' employees.txt
This fails because | is seen as a pipe.Correct:
awk -F "|" '{ print $1 }' employees.txt
# or
awk -F \| '{ print $1 }' employees.txt
The image shows a tip about using the awk command with a field separator, suggesting to enclose the character in double quotes for literal values. There's also a lightbulb icon and a checkmark.

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4. Common Field Separators

SeparatorShell MeaningExample Use Case
:None/etc/passwd
,NoneCSV export
|Pipe (must escape)Database output
\tTab (escape \t)TSV files
=Assignment (escape)Key-value configs
The image shows a list of special characters separated by dotted lines, under the heading "awk -F - Field Separator."

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5. Example: Processing Database Output

Here’s a Bash script (db.sh) that runs a PostgreSQL query inside Docker, trimming each field: 
#!/usr/bin/env bash
docker_run() {
  docker exec -i employees_db psql -U postgres -d employees -tAQ <<EOF
SELECT
  trim(id_employee::text),
  trim(first_name),
  trim(last_name),
  trim(area),
  trim(job_title),
  trim(email),
  trim(salary::text)
FROM "employee";
EOF
}
docker_run > employees.txt
exit 0
View the output: 
$ cat employees.txt

1|Kriti|Shreshtha|Finance|Financial Analyst|[email protected]|60000
...
Extract first names (field 2): 
$ awk -F "|" '{ print $2 }' employees.txt

Kriti
Rajasekar
Debbie
...
See the GNU Awk User’s Guide for more awk options.

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Next Steps

Next, we’ll explore the -v option to declare variables within awk: 
usage: awk [-F fs] [-v var=value] [-f progfile | 'prog'] [file ...]

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References

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