Here's the opposite of your approach, using only basic POSIX shell techniques... #!/bin/sh # trim left space triple ' '* lt() { s="$1"; while [ ! "${s

Here's the opposite of your approach, using only basic POSIX shell techniques... #!/bin/sh # trim left space triple ' '* lt() { s="$1"; while [ ! "${s## }" = "$s" ]; do s="${s## }"; done; printf "%s" "$s"; } # trim right space ' '* rt() { s="$1"; while [ ! "${s%% }" = "$s" ]; do s="${s%% }"; done; printf "%s" "$s"; } # count months for first/last special treatment n=1 # usage: reform pos line1 line2 ... line7 reform() { o=$1; m="$(printf "%s" $(expr substr "$2" $o 20))"; l1="$(expr substr "$3" $o 20)" [ $n -ne 1 ] && l1="$(lt "$l1")" # suffix of spliced week shift 3 printf "%s %s\n" "$l1" "$m" while [ "$#" -gt 0 ]; do l="$(expr substr "$1" $o 20 )"; lx="$(rt "$l")"; shift if [ -z "$lx" ]; then : elif [ "$l" = "$lx" -o $n -eq 12 ]; then printf "%s\n" "$lx" # whole week elif [ -n "$lx" ]; then printf "%s " "$lx" # prefix of spliced week fi done n=$(( $n + 1 )) } # buffer 8 lines into arg vector via recursion hack # then replace lines 3x to project out 3 months in this row buffer() { if [ "$#" -eq 7 ]; then reform 1 "$@"; reform 24 "$@"; reform 47 "$@" else IFS= read line || return 1 [ "$#" -eq 0 ] && read discard buffer "$@" "$line" fi } # strip preamble and process 4 rows of months process() { read discard; read discard; for i in 1 2 3 4; do buffer; done; } cal -y ${1:-2021} | process