Miscellaneous Shell Notes (3)

07/26/23 Corrected typos

07/27/23 Added command

BC

Short for Basic Calculator, this is a calculator provided in accordance with the POSIX standard and available on Unix-based systems.

Key features include:

• Stack-based structure

• Support for Reverse Polish notation (RPN)

echo '2 + 3' | dc
dc <<< '2 3 + p'

TR

A command that enables character conversion, deletion, and compression. It is typically used in conjunction with additional processes via a pipeline.

*tr [문자열1] [문자열2]

: Takes two strings of equal length and replaces the corresponding characters in string 1 with the characters at the same indices in string 2.

• -c: Replaces all characters not present in the second set with the last character of that set.

• -s: Removes all repeating sequences and replaces them with a specified character.

• -d: Removes the specified character.

• -t: Trims both strings to match their lengths before executing the command.

SED (

)

A command that supports various editing functions. It operates primarily on a buffer, so the original file remains unaffected until modifications are applied.

Command Options

• Patterns are expressed in the form /[pattern]/.

• Add -g to process all matching patterns.

• Use commas (,) to specify ranges.

• p: Prints all lines and prints an additional line for each pattern match

  • Add the -n option: Excludes default output; prints only lines matching the pattern

• d: Deletes the pattern

• s: Replaces the pattern

• e: Edit mode

*n;

: Next line

• y: Y-confirmation

• i: Insert

• c: Change

• a: Append

# 약간의 응용

sed -n 'n; p': 짝수 줄 출력
sed -n 'p; n': 홀수 줄 출력

WC

Word Count

• -l: Check the number of lines in the file

• -c: Check the number of bytes in the file

• -m: Check the number of characters in the file

• -w: Check the number of words in the file