Linux Utilities

wc is a utility for counting words, newlines, bytes. Commonly we use it for counting lines.

wc -l will count how many lines (-l argument)

sort will sort the output in alphabetical order

uniq limits the occurences of the same record to only one

less file pager head to show the first 10 lies tail to show the last 10 lines -n to specify

cat dumps text file contents on screen -A shows all non-printable characters -b numbers lines -s supresses repeated lines

tac Shows the text order inverted

sort: (Ordering Output)

n -> Sorts numerically rather than alphabetically
r -> Reverses the sort order
k -> Sorts based on a specific column or key

sort -t: -k3n /etc/passwd

cut (Extracting Columns)

d -> Specifies the delimiter. The character that separates the columns
f -> Specifies the field (column) number you want

cut -d: -f 1 /etc/passwd

tr (Translating Characters)

d -> Deletes the specified characters entirely
s -> Squeezes repeating characters into a single character
echo hello | tr [:lower] [:upper]

grep

grep [opciones] 'patron_a_buscar' archivo.txt

i Ignore case
v Invert match
r R Recursive
n Line number
E Extended regex
B5 Shows the line but also the five in front of it

Text where anna is only at the begining of the word

grep ^anna /etc/password

Shows all lines that end with ash

grep ash$ /etc/passwd

. Wildcard (Matches any single character) [abc] Matches a, b, c ? 0 o 1 + 1 o + * 0 to infinite \{2\} Matches exactly two of the previous character \{1,3\} Matches a minimum of one or a maximum of three of the previous character colou?r Matches zero or one of the previous character (...) Used to group multiple characters so that the regular expression can be applied to the group \b end word

awk -> Tool specialized in data extraction and reporting

By default, awk has a built-in rule: it treats any contiguous sequence of whitespace (spaces and/or tabs) as a single separator.

$1, $2, etc. -> Specific fields (columns).

Examples:

awk 'pattern { action }' file

awk -F : `{print $4}

$NF -> The number of fields (The last column) -F -> Changes the separator

awk -F ':' '/bash/ {print $1}' /etc/passwd

Sed -> Stream editor, used to search and transform text

It can be used to search for text, and perform an operation on matching text

sed 's/texto_a_buscar/texto_nuevo/flags' archivo.txt

flags: g -> Global substitute

Elimina la segunda línea:

sed -i -e '2d' regexes

Imprimir la quinta línea

sed -n '5p' archivo.txt