主页 / coding / 问题 / 79308428
Accepted
gcb
Asked: 2024-12-26 07:16:13 +0800 CST

bash 循环命令中的引号如何影响控制流？

  • 772

看到一些让我怀疑自己理智的事情：

#!/bin/env bash
set -e
for d in '/tmp/somedir/*'; do               
    for f in "${d}/*pub"; do
        echo $f;
    done
done

它按预期返回

/tmp/somedir/AAA/fileaa.pub /tmp/somedir/BBB/filebb.pub

但是，如果我改为echo $f或echo "$f"我echo "${f}"得到：

/tmp/somedir/*/*pub

我很难理解为什么。首先，这是一个单独的项目，所以它不只是影响生产echo线的东西。

使用GNU bash, version 5.2.37(1)-release (x86_64-pc-linux-gnu)

这是该主机上的商店

assoc_expand_once       off
cdable_vars     off
cdspell         off
checkhash       off
checkjobs       off
checkwinsize    on
cmdhist         on
compat31        off
compat32        off
compat40        off
compat41        off
compat42        off
compat43        off
compat44        off
complete_fullquote      on
direxpand       off
dirspell        off
dotglob         off
execfail        off
expand_aliases  on
extdebug        off
extglob         on
extquote        on
failglob        off
force_fignore   on
globasciiranges on
globskipdots    on
globstar        off
gnu_errfmt      off
histappend      on
histreedit      off
histverify      off
hostcomplete    off
huponexit       off
inherit_errexit off
interactive_comments    on
lastpipe        off
lithist         off
localvar_inherit        off
localvar_unset  off
login_shell     off
mailwarn        off
no_empty_cmd_completion off
nocaseglob      off
nocasematch     off
noexpand_translation    off
nullglob        off
patsub_replacement      on
progcomp        on
progcomp_alias  off
promptvars      on
restricted_shell        off
shift_verbose   off
sourcepath      on
varredir_close  off
xpg_echo        off
bash

1 个回答

  1. Best Answer
    #!/bin/env bash
set -e
for d in '/tmp/somedir/*'; do # `*` and `?` should not be quoted unless they exist in the filenames
    for f in "${d}/*pub"; do
        echo $f; # Here, the variable `f` is actually `/tmp/somedir/*/*pub`
                 # Without double quotes, Bash will expand the glob at this point
                 # So, you will see all matching files.
                 # With double quotes, you will see the original value of var `f`
    done
done

    修正脚本后：

    #!/bin/env bash
set -e
for d in /tmp/somedir/*; do               
    for f in "${d}"/*pub; do # only quote the variable
        echo "$f"; # you will get each filename
    done
done

    通常，我们不应该在循环中引用*或?。这样，Bash 将扩展它们以匹配每个文件名，并且 for 循环将按预期运行。

    • 3

相关问题