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Linux - File System: File Content

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Displaying File Content

Command Desc
cat file_name Display all contents
cat -n file_name Display all contents with line numbers
more file_name Browse through a text file.
less file More features than more.
head file Output the first 10 line from the beginning of the file
head -50 file Output the first 50 line from the beginning of the file
tail file Output the last 10 line from the ending of the file
tail -50 file Output the last 50 line from the ending of the file
tail -f file Display data as it is being written to the file
strings Display binary into human readable strings.

Searching Content in Files

Command Desc
grep pattern file Display lines matching a pattern
grep -i pattern file Perform a search, ignoring case.
grep -c pattern file Count the number of occurrences in a file.
grep -n pattern file Precede output with line numbers.
grep -v pattern file Invert Match. Print lines that don’t match.
cut -d'delimiter' file Use delimiter as the field separator.
cut -fN file Display the Nth field. 
cut -d" " -f1 file1
# facebook
# Instagram
# Twitter
# LinkedIn
# TikTok
# Snapchat
# Reddit
# Pinterest
# YouTube
# WhatsApp

cat file1 | grep -i music | cut -d' ' -f1
# TikTok

Search a user name in /etc/passwd

grep -i rheladmin /etc/passwd | cut -d: -f1,5 | sort | tr ":" " " | column -t

Filtering Text File Data

CMD DESC
grep "pattern" filename Search for a Simple Word
grep "^pattern" filename Matches lines beginning with
grep "pattern$" filename Matches lines ending with
grep "[0-9]" filename Match Lines with Digits
grep -E "error\|warning" filename Match Multiple Patterns
grep "pattern" file1 file2 Search in Multiple Files
grep -r "pattern" /path/to/directory Recursive Search in Directories
grep -l "pattern" -r /direcotry List only filenames with matches.
grep -v "pattern" filename Invert match: show lines that do not match the pattern.
grep -i "pattern" filename Case-Insensitive Search
grep -n "pattern" filename Show Line Numbers
grep -w "pattern" filename Match whole words only.
grep -c "pattern" filename Count the number of matching lines.
grep -o "pattern" filename Print only the matched part of the line.
grep -A NUM "pattern" filename Show NUM lines after a match.
grep -B NUM "pattern" filename Show NUM lines before a match.
grep -C NUM "pattern" filename Show NUM lines of context (before and after).
egrep "pattern" file1.txt file2.txt Match Patterns in Multiple Files
egrep "error\| warning\|critical" file.txt Searches for lines containing any of the words.
egrep -i "pattern" file.txt Ignore Case
egrep -v "pattern" file.txt Show lines that do not match the pattern.
egrep -n "pattern" file.txt Display line numbers with the matching lines.
egrep -c "pattern" file.txt Count the Number of Matches
egrep "a{3}" file.txt Match a Specific Number of Repetitions
egrep "colou?r" file.txt the u? makes the “u” optional.
egrep "file-+" file.txt Match “file-“ followed by one or more hyphens
egrep -A NUM "pattern" filename Show NUM lines after a match.
egrep -B NUM "pattern" filename Show NUM lines before a match.
egrep -C NUM "pattern" filename Show NUM lines of context (before and after).

Sorting Text File Data

Command Desc
sort file sort from a file and display
sort file -o newfile sort and write result to FILE
sort -kF file sort via a key. F: the field number
sort -r file sort in reverse order
sort -u file sort unique
sort -n file sort by string numerical value 
cat > txtfile <<EOF
tags: credentials
site: facebook.com
user: bob
pass: Abee!
tags: credentials
EOF
cat txtfile

sort txtfile
# pass: Abee!
# site: facebook.com
# tags: credentials
# tags: credentials
# user: bob

sort -u txtfile
# pass: Abee!
# site: facebook.com
# tags: credentials
# user: bob

sort -ru txtfile
# user: bob
# tags: credentials
# site: facebook.com
# pass: Abee!

sort -u -k2 txtfile
# pass: Abee!
# user: bob
# tags: credentials
# site: facebook.com

Text File Statistics

Command Desc
wc text_file Display newline, word, and byte counts for each file.
wc -c text_file Display byte counts for each file.
wc -m text_file Display character counts for each file.
wc -w text_file Display word counts for each file.
wc -l text_file Display newline counts for each file. 
wc /etc/profile
# 78  247 1899 /etc/profile

# Display newline counts
wc -l /etc/profile
# 78 /etc/profile

# Display word counts
wc -w /etc/profile
# 247 /etc/profile

# Display character counts
wc -m /etc/profile
# 1899 /etc/profile

# Display byte counts
wc -c /etc/profile
# 1899 /etc/profile

Comparing Files

Command Desc
diff file1 file2 Compare two files line by line.
sdiff file1 file2 Side-by-side comparison. using \|
vimdiff file1 file2 Highlight differences in vim. 
diff file1 file2
# 1,2c1
# < facebook
# < Instagram
# ---
# > Facebook
# 5c4
# < TikTok
# ---
# > 1TikTok
# 8d6
# < Pinterest

Note:

  • 1,2c1: line 1,2 of file1 get changed from line 1 of file2
  • 8d6: file1’s line 8 have been deleted from file2’s line6

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