Kategori: OpenSUSE

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Search text files with grep

How to use the grep tool

The grep tool is built into the operating system, so you don’t need to install it.

The simplest syntax to find a string in a single file using the grep command is:
grep ‘searched-word’ filename

By default, the search with grep is case sensitive.

Let’s gradually add the most useful options to our search.

1. Make the search case-insensitive with the "-i" option:
grep -i 'searched-word' filename
2. Search recursively in all files in a given directory with the "-r" option:
grep -ir 'searched-word' '/directory'
3. Search whole words only with the "-w" option:
grep -irw 'searched-word' '/directory'
4. Print the line numbers in which the searched word was found with the "-n" option:
grep -irwn 'searched-word' '/directory'
5. Search for multiple words syntax:
grep -ir 'word1|word2|word3' '/directory'

Many other useful grep options can be found in the official Grep Manual.

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Swap area in OpenSUSE

First create an 1Gigabyte file.

opensuse:~# dd if=/dev/zero of=/swap   bs=1024 count=1000000
1000000+0 records in
1000000+0 records out
1024000000 bytes (1.0 GB) copied, 28.7256 s, 35.6 MB/s

DD command to create the 1G file basically writing “0” into the file swap_1 in the “/” file system.

Create SWAP area

opensuse:~ # mkswap /swap
Setting up swapspace version 1, size = 999996 KiB
no label, UUID=4aada58e-d6f7-4053-adf1-8d4c79122d36

That sets up the file as a swap area.

Now, we’ll simply enable the swapfile, so that the system can start paging physical memory pages onto it.

opensuse:~ # swapon /swap

The system should now have an additional 1Gigabyte of swap area. Check it.

opensuse:~ # free -tom
total       used       free     shared    buffers     cached
Mem:           998        973         24          0         20        795
Swap:         1716          0       1716
Total:        2714        973       1741

We now have 1.7Gigabytes of swap area.

To confirm the swap areas we have

opensuse:~ # swapon -s
Filename                                Type            Size    Used    Priority
/dev/mapper/system-swap                 partition       757752  0       -1
/swap                                      file            999992  0       -2

To make it permanent, we need to add an entry to the /etc/fstab file.:

/swap       swap                 swap       defaults              0 0

Where /swap is our new swap file and it instructs the system to mount it at system startup as a swap area.