> ## Documentation Index
> Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Option F
> Learn to use the -F option in awk to customize field separators for processing structured text.
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.
```bash theme={null}
usage: awk [-F fs] [-v var=value] [-f progfile | 'prog'] [file ...]
```
## 1. Default Field Splitting
By default, `awk` treats any whitespace as the field separator:
```bash theme={null}
$ df -h
```
```text theme={null}
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.
## 2. Changing the Field Separator with -F
To use a colon (`:`) as the separator:
```bash theme={null}
$ awk -F ":" '{ print $1 }' sizeV1.txt
```
```text theme={null}
Filesystem
udev
tmpfs
/dev/sda1
...
```
Print the second field:
```bash theme={null}
$ awk -F ":" '{ print $2 }' sizeV1.txt
```
```text theme={null}
Size
1.8G
366M
...
```
Combine fields 1 and 5:
```bash theme={null}
$ awk -F ":" '{ print $1, $5 }' sizeV1.txt
```
```text theme={null}
Filesystem Use%
udev 0%
tmpfs 3%
...
```
You can also pipe data into `awk`:
```bash theme={null}
$ cat sizeV1.txt | awk -F ":" '{ print $2 }'
```
## 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:
```bash theme={null}
awk -F | '{ print $1 }' employees.txt
```
This fails because `|` is seen as a pipe.
Correct:
```bash theme={null}
awk -F "|" '{ print $1 }' employees.txt
# or
awk -F \| '{ print $1 }' employees.txt
```
## 4. Common Field Separators
| Separator | Shell Meaning | Example Use Case |
| --------- | ------------------- | ----------------- |
| : | None | `/etc/passwd` |
| , | None | CSV export |
| \| | Pipe (must escape) | Database output |
| \t | Tab (escape \t) | TSV files |
| = | Assignment (escape) | Key-value configs |
## 5. Example: Processing Database Output
Here’s a Bash script (`db.sh`) that runs a PostgreSQL query inside Docker, trimming each field:
```bash theme={null}
#!/usr/bin/env bash
docker_run() {
docker exec -i employees_db psql -U postgres -d employees -tAQ < employees.txt
exit 0
```
View the output:
```bash theme={null}
$ cat employees.txt
```
```text theme={null}
1|Kriti|Shreshtha|Finance|Financial Analyst|kriti.shreshtha@company.com|60000
...
```
Extract first names (field 2):
```bash theme={null}
$ awk -F "|" '{ print $2 }' employees.txt
```
```text theme={null}
Kriti
Rajasekar
Debbie
...
```
See the [GNU Awk User’s Guide](https://www.gnu.org/software/gawk/manual/html_node/Options.html) for more `awk` options.
## Next Steps
Next, we’ll explore the **-v** option to declare variables within `awk`:
```bash theme={null}
usage: awk [-F fs] [-v var=value] [-f progfile | 'prog'] [file ...]
```
## References
* [GNU Awk Manual](https://www.gnu.org/software/gawk/manual/)
* [awk(1) — Linux manual page](https://man7.org/linux/man-pages/man1/awk.1.html)
* [PostgreSQL Documentation](https://www.postgresql.org/docs/)