Command Lines

echo [-neE] [ARGUMENTS]

• -e interpert escaped-character
• -E Not interpert escaped-character (by default)

• Display output of command echo $(command)

  > echo "The date is: $(date +%D)"
  The data is '04/13/2020'

• Display variable echo $USER

  Andrew Chen

tail

• -n: If you put a plus sign before num, tail outputs all lines beginning with that line. For example, -n +1 prints every line.

grep [OPTION] [COND] FILE

• -E regex matching
• -s replaces repeated characters listed in the set1 with single occurrence
• --color add color for matching element

awk

awk '{ print $2 }'
awk '{ gsub(/[:]/, ".*:") } { print $1":[0-9]+"};'

cut [OPTION] [FILE]

• -f(--field) Select by specifying a field, a set of fields, or a range of fields, which separated by,.
  Can set delimiter by using -d. Otherwise, it’ll use TAB by default.

  • -d(--delimiter) Specify a delimiter that will be used instead of the default TAB delimiter.
  • -s(--only-delimited) Cut doesn’t print lines not containing delimiters.

#input.txt
Hello World
Happy New World
World

> cut -f1 -d ' ' input.txt
Hello
Happy
World

> cut -f1,2 -d ' ' input.txt
Hello World
Happy New
World

> cut -f1 -d ' ' -s input.txt
Hello
Happy

sed

sed 's/.$//'

xargs

tr [OPTION] SET1 [SET2]

• -d delete characters in the first set from the output
• -s replaces repeated characters listed in the set1 with single occurrence

> echo 'aaaaabcd' | tr -s 'a'
abcd

> echo $PATH
/bin:/usr/sbin:/sbin

> echo $PATH | tr ':' '\n'
/bin
/usr/sbin
/sbin

• -c complements the set of characters in strin

sudo su

• Change the current user to root user

• Can achieve by using #

  • e.g. # echo "Hello World" > /sys/...

    tee

• print and output the content to a file (> don’t print the content)