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(Special Shell Variables): Document some

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more LINENO gotchas, particularly with respect to the Awk+Sed hack.
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Paul Eggert 2001-10-26 19:52:07 +00:00
parent 67b5412d75
commit 34d266fd69
1 changed files with 45 additions and 14 deletions
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59
doc/autoconf.texi
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@ -8187,10 +8187,19 @@ builtin @command{unset}, for more details.
@item LINENO
@evindex LINENO
Most modern shells provide the current line number in @code{LINENO}.
Its value is the line number of the beginning of the current command
(see below the output of the here document). The behavior wrt
@command{eval} differs according to the shell, but, amusingly, not in
the case of sub shells:
Its value is the line number of the beginning of the current command.
Autoconf attempts to execute @command{configure} with a modern shell.
If no such shell is available, it attempts to implement @code{LINENO}
with a simple Awk+Sed prepass that replaces the first instance of the
string @code{$LINENO} in each line with the line's number.
You should not rely on @code{LINENO} within @command{eval}, as the
behavior differs in practice. Also, the possibility of the Awk+Sed
prepass means that you should not rely on @code{$LINENO} when quoted,
when in here-documents, or when in long commands that cross line
boundaries or that have multiple instances of $LINENO. Subshells
should be OK, though. In the following example, lines 1, 6, and 10
are portable, but the other instances of @code{LINENO} are not:
@example
@group
@ -8202,30 +8211,34 @@ cat <<EOF
EOF
( echo 6. $LINENO )
eval 'echo 7. $LINENO'
echo 8. $LINENO $LINENO
echo 9. '$LINENO'
echo 10. $LINENO '
11.' $LINENO
@end group
@group
$ @kbd{ash lineno}
1.
3.
4.
6.
7.
@end group
@group
$ @kbd{bash-2.03 lineno}
$ @kbd{bash-2.05 lineno}
1. 1
3. 2
4. 2
6. 6
7. 1
8. 8 8
9. $LINENO
10. 10
11. 10
@end group
@group
$ @kbd{zsh-3.1.9 lineno}
$ @kbd{zsh-3.0.6 lineno}
1. 1
3. 2
4. 2
6. 6
7. 7
8. 8 8
9. $LINENO
10. 10
11. 10
@end group
@group
$ @kbd{pdksh-5.2.14 lineno}
@ -8234,6 +8247,24 @@ $ @kbd{pdksh-5.2.14 lineno}
4. 2
6. 6
7. 0
8. 8 8
9. $LINENO
10. 10
11. 10
@end group
@group
$ @kbd{awk '/\$LINENO/@{printf "%d:", NR@}; @{print@}' lineno |}
> @kbd{sed '/\$LINENO/s/^\([^:]*\):\(.*\)\$LINENO/\2\1/' |}
> @kbd{sh}
1. 1
3. 3
4. 4
6. 6
7. 7
8. 8
9. 9
10. 10
11. 11
@end group
@end example