cut
pode ser útil:
$ echo hello | cut -c1,3
hl
$ echo hello | cut -c1-3
hel
$ echo hello | cut -c1-4
hell
$ echo hello | cut -c4-5
lo
O Shell Builtins também é bom para isso, aqui está um exemplo de script:
#!/bin/bash
# Demonstrates shells built in ability to split stuff. Saves on
# using sed and awk in shell scripts. Can help performance.
shopt -o nounset
declare -rx FILENAME=payroll_2007-06-12.txt
# Splits
declare -rx NAME_PORTION=${FILENAME%.*} # Left of .
declare -rx EXTENSION=${FILENAME#*.} # Right of .
declare -rx NAME=${NAME_PORTION%_*} # Left of _
declare -rx DATE=${NAME_PORTION#*_} # Right of _
declare -rx YEAR_MONTH=${DATE%-*} # Left of _
declare -rx YEAR=${YEAR_MONTH%-*} # Left of _
declare -rx MONTH=${YEAR_MONTH#*-} # Left of _
declare -rx DAY=${DATE##*-} # Left of _
clear
echo " Variable: (${FILENAME})"
echo " Filename: (${NAME_PORTION})"
echo " Extension: (${EXTENSION})"
echo " Name: (${NAME})"
echo " Date: (${DATE})"
echo "Year/Month: (${YEAR_MONTH})"
echo " Year: (${YEAR})"
echo " Month: (${MONTH})"
echo " Day: (${DAY})"
Essa saída:
Variable: (payroll_2007-06-12.txt)
Filename: (payroll_2007-06-12)
Extension: (txt)
Name: (payroll)
Date: (2007-06-12)
Year/Month: (2007-06)
Year: (2007)
Month: (06)
Day: (12)
E, de acordo com o Gnudif acima, há sempre sed / awk / perl para quando as coisas ficam realmente difíceis.