Linux Basics

Sed

Replace the first occurrence of a string in a file, and print the result

sed 's/find/replace/' filename

Replace all the occurrences of a string in a file, and print the result

sed 's/find/replace/g' filename

Replace all occurrences of an extended regular expression in a file

sed -E 's/regular_expression/replace/g' filename

Replace in place all the occurrences of a string in a file and overwrite the file

sed -i '' 's/find/replace/g' filename

Add prefix to all files

sed -i '1s/^/# Copyright (c) MIT License\n\n/' *

Replace only on lines matching the line pattern

sed '/line_pattern/s/find/replace/' filename

Print only text between n-th line till the next empty line:

sed -n 'line_number,/^$/p' filename

Apply multiple find-replace expressions to a file:

sed -e 's/find/replace/' -e 's/find/replace/' filename

Replace separator / by any other character not used in the find/replace patterns, e.g. ;

sed 's;find;replace;' filename
sed '\;deleteme;d' filename

Replacing Newlines with sed

sed ':a;N;$!ba;s/\n//g' filename

Delete the line at the specific line number in a file:

• Any line number: sed '<line_number>d' filename
• First line: sed '1d' filename
• Last line: sed '$d' filename
• Multiple lines: sed '1d;3d;5d' filename
• Exclude lines: sed '1,3!d' filename
• Delete empty lines in a file: sed '/^$/d’ filename

Find

The find command is an indispensable tool in the Linux toolkit, offering unparalleled ability to search and manipulate files across complex directory hierarchies. From finding files by name to searching based on file attributes or sizes, find does it all.

Understanding Basic Syntax

The basic syntax of find is straightforward: find [path] [options]. For instance, to find all .txt files in the current directory, you’d use:

Advanced Search Criteria

find goes beyond simple name searches. You can use it to locate files modified within a specific timeframe, such as files changed in the last 7 days:

Or, find files with specific permissions:

Executing Actions on Found Files

One of the most powerful aspects of find is executing actions on the files it locates. For example, to delete all .tmp files:

Optimizing Search Performance

To enhance performance, limit the search depth. For instance, to search only the current and immediate subdirectories:

Real-World Scenarios and Examples

In practical scenarios, find can be a lifesaver. Imagine you need to locate all JPEG files over 5MB in size and move them to a separate directory. You can accomplish this with a single command:

Tail

Displays the end of a file.

tail -f continuously monitors a file for new lines, great for monitoring log files in real-time.

Head

Shows the beginning of a file.

Specify the number of lines to display (e.g., head -n 5 for the first 5 lines).

Sort

Sorts the contents of a file.

Can sort numerically (-n), reverse order (-r), or even sort by a specific column (-k).

Tee

Reads from standard input and writes to standard output and files simultaneously.

Useful for logging the output of a command to a file while also displaying it (e.g., ls | tee output.txt).

Xargs

Builds and executes command lines from standard input.

Great for combining with other commands to process a list of items, like files or strings. For example, find . -type f | xargs grep "searchTerm" to search for a term in multiple files.