Nel mio .profile, chiamo uno script per determinare la larghezza di una stringa su un terminale. Lo uso quando eseguo l'accesso sulla console di una macchina in cui non mi fido del set di sistemi LC_CTYPEo quando accedo in remoto e non posso fidarmi LC_CTYPEdi abbinare il lato remoto. Il mio script interroga il terminale, piuttosto che chiamare qualsiasi libreria, perché quello era il punto nel mio caso d'uso: determinare la codifica del terminale.
Questo è fragile in diversi modi:
- modifica il display, quindi non è un'esperienza utente molto piacevole;
- c'è una condizione di gara se un altro programma mostra qualcosa nel momento sbagliato;
- si blocca se il terminale non risponde. (Qualche anno fa ho chiesto come migliorare , ma in pratica non è stato un grosso problema, quindi non sono mai riuscito a passare a quella soluzione. L'unico caso che ho riscontrato di un terminale che non rispondeva era un Windows Emacs che accede ai file remoti da una macchina Linux con il
plinkmetodo e l'ho risolto usando plinkxinvece il metodo .)
Questo potrebbe corrispondere o meno al tuo caso d'uso.
#! /bin/sh
if [ z"$ZSH_VERSION" = z ]; then :; else
emulate sh 2>/dev/null
fi
set -e
help_and_exit () {
cat <<EOF
Usage: $0 {-NUMBER|TEXT}
Find out the width of TEXT on the terminal.
LIMITATION: this program has been designed to work in an xterm. Only
xterm and sufficiently compatible terminals will work. If you think
this program may be blocked waiting for input from the the terminal,
try entering the characters "0n0n" (digit 0, lowercase letter n,
repeat).
Display TEXT and erase it. Find out the position of the cursor before
and after displaying TEXT so as to compute the width of TEXT. The width
is returned as the exit code of the program. A value of 100 is returned if
the text is wider than 100 columns.
TEXT may contain backslash-escapes: \\0DDD represents the byte whose numeric
value is DDD in octal. Use '\\\\' to include a single backslash character.
You may use -NUMBER instead of TEXT (if TEXT begins with a dash, use
"-- TEXT"). This selects one of the built-in texts that are designed
to discriminate between common encodings. The following table lists
supported values of NUMBER (leftmost column) and the widths of the
sample text in several encodings.
1 ASCII=0 UTF-8=2 latinN=3 8bits=4
EOF
exit
}
builtin_text () {
case $1 in
-*[!0-9]*)
echo 1>&2 "$0: bad number: $1"
exit 119;;
-1) # UTF8: {\'E\'e}; latin1: {\~A\~A\copyright}; ASCII: {}
text='\0303\0211\0303\0251';;
*)
echo 1>&2 "$0: there is no text number $1. Stop."
exit 118;;
esac
}
text=
if [ $# -eq 0 ]; then
help_and_exit 1>&2
fi
case "$1" in
--) shift;;
-h|--help) help_and_exit;;
-[0-9]) builtin_text "$1";;
-*)
echo 1>&2 "$0: unknown option: $1"
exit 119
esac
if [ z"$text" = z ]; then
text="$1"
fi
printf "" # test that it is there (abort on very old systems)
csi='\033['
dsr_cpr="${csi}6n" # Device Status Report --- Report Cursor Position
dsr_ok="${csi}5n" # Device Status Report --- Status Report
stty_save=`stty -g`
if [ z"$stty_save" = z ]; then
echo 1>&2 "$0: \`stty -g' failed ($?)."
exit 3
fi
initial_x=
final_x=
delta_x=
cleanup () {
set +e
# Restore terminal settings
stty "$stty_save"
# Restore cursor position (unless something unexpected happened)
if [ z"$2" = z ]; then
if [ z"$initial_report" = z ]; then :; else
x=`expr "${initial_report}" : "\\(.*\\)0"`
printf "%b" "${csi}${x}H"
fi
fi
if [ z"$1" = z ]; then
# cleanup was called explicitly, so don't exit.
# We use `trap : 0' rather than `trap - 0' because the latter doesn't
# work in older Bourne shells.
trap : 0
return
fi
exit $1
}
trap 'cleanup 120 no' 0
trap 'cleanup 129' 1
trap 'cleanup 130' 2
trap 'cleanup 131' 3
trap 'cleanup 143' 15
stty eol 0 eof n -echo
printf "%b" "$dsr_cpr$dsr_ok"
initial_report=`tr -dc \;0123456789`
# Get the initial cursor position. Time out if the terminal does not reply
# within 1 second. The trick of calling tr and sleep in a pipeline to put
# them in a process group, and using "kill 0" to kill the whole process
# group, was suggested by Stephane Gimenez at
# /unix/10698/timing-out-in-a-shell-script
#trap : 14
#set +e
#initial_report=`sh -c 'ps -t $(tty) -o pid,ppid,pgid,command >/tmp/p;
# { tr -dc \;0123456789 >&3; kill -14 0; } |
# { sleep 1; kill -14 0; }' 3>&1`
#set -e
#initial_report=`{ sleep 1; kill 0; } |
# { tr -dc \;0123456789 </dev/tty; kill 0; }`
if [ z"$initial_report" = z"" ]; then
# We couldn't read the initial cursor position, so abort.
cleanup 120
fi
# Write some text and get the final cursor position.
printf "%b%b" "$text" "$dsr_cpr$dsr_ok"
final_report=`tr -dc \;0123456789`
initial_x=`expr "$initial_report" : "[0-9][0-9]*;\\([0-9][0-9]*\\)0" || test $? -eq 1`
final_x=`expr "$final_report" : "[0-9][0-9]*;\\([0-9][0-9]*\\)0" || test $? -eq 1`
delta_x=`expr "$final_x" - "$initial_x" || test $? -eq 1`
cleanup
# Zsh has function-local EXIT traps, even in sh emulation mode. This
# is a long-standing bug.
trap : 0
if [ $delta_x -gt 100 ]; then
delta_x=100
fi
exit $delta_x
Lo script restituisce la larghezza nel suo stato di ritorno, tagliato a 100. Esempio di utilizzo:
widthof -1
case $? in
0) export LC_CTYPE=C;; # 7-bit charset
2) locale_search .utf8 .UTF-8;; # utf8
3) locale_search .iso88591 .ISO8859-1 .latin1 '';; # 8-bit with nonprintable 128-159, we assume latin1
4) locale_search .iso88591 .ISO8859-1 .latin1 '';; # some full 8-bit charset, we assume latin1
*) export LC_CTYPE=C;; # weird charset
esac