74d9b02bb0
Before considering to execute a command substitution in the same process,
check if any of the expansions may have a side effect; if so, execute it in
a new process just like happens if it is not a single simple command.
Although the check happens at run time, it is a static check that does not
depend on current state. It is triggered by:
- expanding $! (which may cause the job to be remembered)
- ${var=value} default value assignment
- assignment operators in arithmetic
- parameter substitutions in arithmetic except ${#param}, $$, $# and $?
- command substitutions in arithmetic
This means that $((v+1)) does not prevent optimized command substitution,
whereas $(($v+1)) does, because $v might expand to something containing
assignment operators.
Scripts should not depend on these exact details for correctness. It is also
imaginable to have the shell fork if and when a side effect is encountered
or to create a new temporary namespace for variables.
Due to the $! change, the construct $(jobs $!) no longer works. The value of
$! should be stored in a variable outside command substitution first.
68 lines
2.6 KiB
C
68 lines
2.6 KiB
C
/*-
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* Copyright (c) 1991, 1993
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* The Regents of the University of California. All rights reserved.
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*
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* This code is derived from software contributed to Berkeley by
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* Kenneth Almquist.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* @(#)expand.h 8.2 (Berkeley) 5/4/95
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* $FreeBSD$
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*/
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struct strlist {
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struct strlist *next;
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char *text;
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};
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struct arglist {
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struct strlist *list;
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struct strlist **lastp;
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};
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/*
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* expandarg() flags
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*/
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#define EXP_FULL 0x1 /* perform word splitting & file globbing */
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#define EXP_TILDE 0x2 /* do normal tilde expansion */
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#define EXP_VARTILDE 0x4 /* expand tildes in an assignment */
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#define EXP_REDIR 0x8 /* file glob for a redirection (1 match only) */
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#define EXP_CASE 0x10 /* keeps quotes around for CASE pattern */
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#define EXP_SPLIT_LIT 0x20 /* IFS split literal text ${v+-a b c} */
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#define EXP_LIT_QUOTED 0x40 /* for EXP_SPLIT_LIT, start off quoted */
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union node;
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void expandhere(union node *, int);
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void expandarg(union node *, struct arglist *, int);
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void expari(int);
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int patmatch(const char *, const char *, int);
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void rmescapes(char *);
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int casematch(union node *, const char *);
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int expandhassideeffects(const char *);
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int wordexpcmd(int, char **);
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