How to Find Commented and Uncommented Lines Using grep and Save the Output to a File

When managing configuration files, it is often necessary to distinguish between commented and un-commented lines. This guide will show you how to use the grep command to find and save commented and uncommented lines in a file.

Finding Commented Lines

Commented lines in a configuration file typically start with a #. You can use grep to search for these lines and save the output to a file.

Explanation:

• ^#: This pattern matches lines that start with #.
• /etc/crontab: The file being searched.
• > commented-lines: Redirects the output to a file named commented-lines.

Example Output:

[root@redhat ~]# grep ^[#] /etc/crontab > commented-lines

To view the saved output:

cat commented-lines

Preview:

[root@redhat ~]# cat commented-lines

# Example of job definition:

# .---------------- minute (0 - 59)

# |  .------------- hour (0 - 23)

# |  |  .---------- day of month (1 - 31)

# |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...

# |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat

# |  |  |  |  |

# *  *  *  *  * user-name  command to be executed

[root@redhat ~]#

Finding Uncommented Lines

Uncommented lines do not start with a #. You can use grep to search for these lines and save the output to a file.

Explanation:

• ^[^#]: This pattern matches lines that do not start with #.
• /etc/crontab: The file being searched.
• > un-commented-lines: Redirects the output to a file named un-commented-lines.

Example Output:

[root@redhat ~]# grep ^[^#] /etc/crontab > un-commented-lines

To view the saved output:

cat un-commented-lines

Preview:

[root@redhat ~]# cat un-commented-lines

SHELL=/bin/bash

PATH=/sbin:/bin:/usr/sbin:/usr/bin

MAILTO=root

 For details see man 4 crontabs

[root@redhat ~]#

Summary

You can use the grep command to filter out commented and uncommented lines from a file and save the results to separate files. This is useful for quickly reviewing and managing configuration settings.

Finding and Saving Commented Lines:

grep ^[#] /etc/crontab > commented-lines

View saved output:

grep ^[^#] /etc/crontab > un-commented-lines

View saved output: