Sort / Compare / Count

Read and insert file content

sed -r <file>

Sort

sort [file]	Alphabetical, ascending
cat [file] | sort	Pipe output to sort.
sort -n	Sort numerically.
sort -r	Reverses the result of comparisons, producing a descending order sort.
sort -k	Specifies a sort key.
sort -k2	Sorts by second column.
sort -k 2n,2	Sorts numerically based on the second field, ignoring leading whitespace in that field.
sort -k 1b	Sorts by the first word in each line, ignoring case distinctions (-b).
sort -u	Outputs only the first of an equal run.
sort -t	Sets the field delimiter.
sort -t ',' -k 2	Sort lines by the second field

Sorts data.csv first by the second field numerically in descending order, then by the first field ignoring case:

sort -k 2n,2r -k 1f data.csv

Sorts ps output by CPU% descending, then by PID (process ID):

ps aux | sort -nrk 3,3 -k 8

Compare

Choosing the right command

diff	For line-by-line text comparison
cmp	For byte-level comparison
comm	For comparing sorted lists
diffstat	For quick statistics
meld	For visual comparison
md5sum	For verifying file integrity
sha256sum	For verifying file integrity

Commands

diff <file1> <file2>	Compare two files line by line.
diff -n <file1> <file2>	Suppresses line numbers.
diff -i <file1> <file2>	Ignore case differences in file contents.
diff -u <file1> <file2>	Produce a unified format diff, showing several lines of context.
diff -q <file1> <file2>	Report only when files differ, without detailing the differences.
diff -w <file1> <file2>	Ignore all whitespace changes.
diff -b <file1> <file2>	Ignore changes in the amount of whitespace.
diff --left-column <file1> <file2>	Show line numbers for differences.
cmp <file1> <file2>	Byte-by-byte comparison.
cmp -l <file1> <file2>	Show all differences between the files.
cmp -s <file1> <file2>	Silent mode, do not write anything, just return an exit status.
comm <file1> <file2>	Compare two sorted files line by line.
comm -1 -2 <file1> <file2>	Suppress output of specified columns (1 and 2), showing only lines common to both files.
diff3 <file1> <file2> file3.txt	Compare three files line by line.
diff3 -m <file1> <file2> file3.txt	Show only conflicting changes among the three files.
sdiff <file1> <file2>	Side-by-side comparison of files.
sdiff -i <file1> <file2>	Ignore case differences in file contents.
sdiff -s <file1> <file2>	Suppress lines common to both files.
diffstat diff_output	Read a diff output file and display a histogram of insertions, deletions, and modifications per file.
meld file1 file2	Graphical tool to compare and merge files interactively.
md5sum file	Calculate MD5 checksum.
sha256sum file	Calculate SHA-256 checksum.

Count

wc [file]	Count lines, words, and bytes.
wc -l [file]	Count lines.
wc -w [file]	Count words.
wc -c [file]	Count bytes.
wc -m [file]	Count characters.
awk 'END {print NR}' [file]	Count lines. NR represents the total number of records processed.
awk '{count++} END {print count}' [file]	Count lines.
awk '/error/ {count++} END {print count}' [file]	Count lines containing "error".
sed '/^$/d' filename | wc -l	Counts non-empty lines.
sed 's/[^a-zA-Z0-9 ]//g' filename | wc -w	Counts alphanumeric words
sed -n '$=' [file]	Count lines. $= command prints the total number of lines.
grep pattern [file] | wc -l	Alternate way to count lines
grep -c "[pattern]" [file]	Lines with pattern match.
grep -c "[pattern]" <file1> <file2>	Miltiple files
grep -o "[pattern]" [file] | wc -l	Count pattern matches, including multiple occurrences per line. -o outputs each match on a new line.
grep -r -c "[pattern]" /directory	Recursive counts lines with pattern match.
find . -type f | wc -l	Count files in a directory and its subdirectories

Recursive by file extension:

grep --include=\*.<ext> -ro "[pattern]" <directory> | wc -l

Recursive counts lines with pattern match:

find / -type f -exec grep -o "[pattern]" {} + | wc -l

Uses awk to globally substitute (thus count) occurrences of the pattern in each line and sums them up:

awk '{count += gsub(/[pattern]/, "[pattern]")} END {print count}' [file]

Count the total number of lines across all files in a directory and its subdirectories:

find . -type f -exec wc -l {} + | awk '{total += $1} END {print total}'