Text files
grep
cat syslog | grep -E ‘2005/07/19 09:00./ivr/common’ | grep -v ‘try_transfer' > sample_nauivrd.log.
sed
Splitting a File into Parts
To split a file into parts where 4646 is the starting line and 9999 is the ending line:
sed -n 4646,9999p old.file > new.file
Display Lines 5-10
To display lines 5 through 10:
sed -n '5,10p' /etc/group
Display All Lines Except 5-10
To display all lines except for lines 5 through 10:
sed -n '5,10d' /etc/group
Substitution Command
The command s/pattern1/pattern2/ is used for substitution. The letter "s" stands for "substitute."
Extracting a Portion of a File
To extract a portion of a file from byte 10001 to 20000:
cat blabla.dump | cut -b 10001-20000 > mumu.dump
Here's a mini-guide on using the tail command in Linux:
tail
The tail command is used to display the last part of a file or stream in Linux. By default, it shows the last 10 lines of a file, but you can customize this behavior with various options.
Basic Usage
To display the last 10 lines of a file:
tail filename
Display a Specific Number of Lines
To display a specific number of lines from the end of a file, use the -n option followed by the number of lines:
tail -n 20 filename
This will display the last 20 lines of the file.
Display the Last N Bytes
If you want to display the last N bytes instead of lines, use the -c option:
tail -c 50 filename
This will display the last 50 bytes of the file.
Follow a File in Real-Time
One of the most powerful features of tail is the ability to follow a file in real-time as new lines are added. This is particularly useful for monitoring log files:
tail -f filename
This command will display the last few lines of the file and continue to output new lines as they are written to the file.
You can combine -f with -n to start from a specific number of lines and continue following:
tail -n 50 -f filename
Stop Following After a Certain Period
If you want to follow a file for a limited amount of time, use the --pid option along with a process ID, or --max-unchanged-stats to stop after a certain period of inactivity:
tail -f filename --pid=1234
Or:
tail -f filename --max-unchanged-stats=5s
Example: Monitoring System Logs
A common use case for tail is monitoring system logs:
tail -f /var/log/syslog
This command will display the latest system log entries as they are added to the file.
Here are mini-guides for the tar and tr commands in Linux:
tar Command in Linux
The tar command is used to create, extract, and manage archive files in Linux. It is commonly used to compress and package multiple files into a single file for easier distribution or backup.
Basic Usage
To create a tar archive:
tar -cvf archive_name.tar directory_or_file
-c: Create a new archive.-v: Verbose mode, shows progress in the terminal.-f: Specifies the filename of the archive.
Compressing an Archive with gzip
To compress the archive using gzip, use the -z option:
tar -czvf archive_name.tar.gz directory_or_file
-z: Compress the archive usinggzip.
Extracting an Archive
To extract a tar archive:
tar -xvf archive_name.tar
-x: Extract files from an archive.
For compressed archives:
tar -xzvf archive_name.tar.gz
Extracting a Specific File
To extract a specific file from a tar archive:
tar -xvf archive_name.tar file_to_extract
List Contents of an Archive
To list the contents of a tar archive without extracting:
tar -tvf archive_name.tar
-t: List the contents of the archive.
Example: Creating and Extracting an Archive
Create a compressed archive:
tar -czvf backup.tar.gz /path/to/directory
Extract the compressed archive:
tar -xzvf backup.tar.gz
tr Command in Linux
The tr command is used to translate or delete characters from the input provided to it. It reads from standard input and writes to standard output, making it useful for various text processing tasks.
Basic Usage
To translate characters, specify the characters to replace and their replacements:
echo "hello world" | tr 'a-z' 'A-Z'
This command converts all lowercase letters to uppercase:
Output:
HELLO WORLD
Delete Specific Characters
To delete specific characters, use the -d option:
echo "hello 123 world" | tr -d '0-9'
This will remove all digits from the text:
Output:
hello world
Replace Multiple Spaces with a Single Space
To replace multiple spaces with a single space:
echo "hello world" | tr -s ' '
-s: Squeeze, which replaces sequences of a character with a single instance.
Output:
hello world
Example: Translating and Deleting Characters
Translate spaces to newlines:
echo "apple orange banana" | tr ' ' '\n'
Delete all vowels from the input:
echo "hello world" | tr -d 'aeiou'
Output:
hll wrld