我正在写一个shell脚本，需要检查终端应用程序是否已安装。我想使用TRY/CATCH命令来做到这一点，除非有更整洁的方法。
当前回答
下面是一个在bash中实现try/catch/finally的脚本示例。
与此问题的其他答案一样，必须在退出子进程后捕获异常。
The example scripts start by creating an anonymous fifo, which is used to pass string messages from a command exception or throw to end of the closest try block. Here the messages are removed from the fifo and placed in an array variable. The status is returned through return and exit commands and placed in a different variable. To enter a catch block, this status must not be zero. Other requirements to enter a catch block are passed as parameters. If the end of a catch block is reached, then the status is set to zero. If the end of the finally block is reached and the status is still nonzero, then an implicit throw containing the messages and status is executed. The script requires the calling of the function trycatchfinally which contains an unhandled exception handler.
trycatchfinally命令的语法如下所示。
trycatchfinally [-cde] [-h ERR_handler] [-k] [-o debug_file] [-u unhandled_handler] [-v variable] fifo function
The -c option adds the call stack to the exception messages. The -d option enables debug output. The -e option enables command exceptions. The -h option allows the user to substitute their own command exception handler. The -k option adds the call stack to the debug output. The -o option replaces the default output file which is /dev/fd/2. The -u option allows the user to substitute their own unhandled exception handler. The -v option allows the user the option to pass back values though the use of Command Substitution. The fifo is the fifo filename. The function function is called by trycatchfinally as a subprocess.
注意:为了简化脚本，删除了cdko选项。
catch命令的语法如下所示。
catch [[-enoprt] list ...] ...
选项定义如下。第一个列表的值是状态。子值是消息。如果有更多的消息 列表，那么其余的消息将被忽略。
-e means [[ $value == "$string" ]] (the value has to match at least one string in the list) -n means [[ $value != "$string" ]] (the value can not match any of the strings in the list) -o means [[ $value != $pattern ]] (the value can not match any of the patterns in the list) -p means [[ $value == $pattern ]] (the value has to match at least one pattern in the list) -r means [[ $value =~ $regex ]] (the value has to match at least one extended regular expression in the list) -t means [[ ! $value =~ $regex ]] (the value can not match any of the extended regular expressions in the list)
try/catch/finally脚本如下所示。为了简化这个答案的脚本，删除了大部分错误检查。这样就减少了64%的尺寸。这个脚本的完整副本可以在我的其他答案中找到。
shopt -s expand_aliases
alias try='{ common.Try'
alias yrt='EchoExitStatus; common.yrT; }'
alias catch='{ while common.Catch'
alias hctac='common.hctaC; done; }'
alias finally='{ common.Finally'
alias yllanif='common.yllaniF; }'
DefaultErrHandler() {
echo "Orginal Status: $common_status"
echo "Exception Type: ERR"
}
exception() {
let "common_status = 10#$1"
shift
common_messages=()
for message in "$@"; do
common_messages+=("$message")
done
}
throw() {
local "message"
if [[ $# -gt 0 ]]; then
let "common_status = 10#$1"
shift
for message in "$@"; do
echo "$message" >"$common_fifo"
done
elif [[ ${#common_messages[@]} -gt 0 ]]; then
for message in "${common_messages[@]}"; do
echo "$message" >"$common_fifo"
done
fi
chmod "0400" "$common_fifo"
exit "$common_status"
}
common.ErrHandler() {
common_status=$?
trap ERR
if [[ -w "$common_fifo" ]]; then
if [[ $common_options != *e* ]]; then
common_status="0"
return
fi
eval "${common_errHandler:-} \"${BASH_LINENO[0]}\" \"${BASH_SOURCE[1]}\" \"${FUNCNAME[1]}\" >$common_fifo <$common_fifo"
chmod "0400" "$common_fifo"
fi
if [[ common_trySubshell -eq BASH_SUBSHELL ]]; then
return
else
exit "$common_status"
fi
}
common.Try() {
common_status="0"
common_subshell="$common_trySubshell"
common_trySubshell="$BASH_SUBSHELL"
common_messages=()
}
common.yrT() {
local "status=$?"
if [[ common_status -ne 0 ]]; then
local "message=" "eof=TRY_CATCH_FINALLY_END_OF_MESSAGES_$RANDOM"
chmod "0600" "$common_fifo"
echo "$eof" >"$common_fifo"
common_messages=()
while read "message"; do
[[ $message != *$eof ]] || break
common_messages+=("$message")
done <"$common_fifo"
fi
common_trySubshell="$common_subshell"
}
common.Catch() {
[[ common_status -ne 0 ]] || return "1"
local "parameter" "pattern" "value"
local "toggle=true" "compare=p" "options=$-"
local -i "i=-1" "status=0"
set -f
for parameter in "$@"; do
if "$toggle"; then
toggle="false"
if [[ $parameter =~ ^-[notepr]$ ]]; then
compare="${parameter#-}"
continue
fi
fi
toggle="true"
while "true"; do
eval local "patterns=($parameter)"
if [[ ${#patterns[@]} -gt 0 ]]; then
for pattern in "${patterns[@]}"; do
[[ i -lt ${#common_messages[@]} ]] || break
if [[ i -lt 0 ]]; then
value="$common_status"
else
value="${common_messages[i]}"
fi
case $compare in
[ne]) [[ ! $value == "$pattern" ]] || break 2;;
[op]) [[ ! $value == $pattern ]] || break 2;;
[tr]) [[ ! $value =~ $pattern ]] || break 2;;
esac
done
fi
if [[ $compare == [not] ]]; then
let "++i,1"
continue 2
else
status="1"
break 2
fi
done
if [[ $compare == [not] ]]; then
status="1"
break
else
let "++i,1"
fi
done
[[ $options == *f* ]] || set +f
return "$status"
}
common.hctaC() {
common_status="0"
}
common.Finally() {
:
}
common.yllaniF() {
[[ common_status -eq 0 ]] || throw
}
caught() {
[[ common_status -eq 0 ]] || return 1
}
EchoExitStatus() {
return "${1:-$?}"
}
EnableThrowOnError() {
[[ $common_options == *e* ]] || common_options+="e"
}
DisableThrowOnError() {
common_options="${common_options/e}"
}
GetStatus() {
echo "$common_status"
}
SetStatus() {
let "common_status = 10#$1"
}
GetMessage() {
echo "${common_messages[$1]}"
}
MessageCount() {
echo "${#common_messages[@]}"
}
CopyMessages() {
if [[ ${#common_messages} -gt 0 ]]; then
eval "$1=(\"\${common_messages[@]}\")"
else
eval "$1=()"
fi
}
common.GetOptions() {
local "opt"
let "OPTIND = 1"
let "OPTERR = 0"
while getopts ":cdeh:ko:u:v:" opt "$@"; do
case $opt in
e) [[ $common_options == *e* ]] || common_options+="e";;
h) common_errHandler="$OPTARG";;
u) common_unhandled="$OPTARG";;
v) common_command="$OPTARG";;
esac
done
shift "$((OPTIND - 1))"
common_fifo="$1"
shift
common_function="$1"
chmod "0600" "$common_fifo"
}
DefaultUnhandled() {
local -i "i"
echo "-------------------------------------------------"
echo "TryCatchFinally: Unhandeled exception occurred"
echo "Status: $(GetStatus)"
echo "Messages:"
for ((i=0; i<$(MessageCount); i++)); do
echo "$(GetMessage "$i")"
done
echo "-------------------------------------------------"
}
TryCatchFinally() {
local "common_errHandler=DefaultErrHandler"
local "common_unhandled=DefaultUnhandled"
local "common_options="
local "common_fifo="
local "common_function="
local "common_flags=$-"
local "common_trySubshell=-1"
local "common_subshell"
local "common_status=0"
local "common_command="
local "common_messages=()"
local "common_handler=$(trap -p ERR)"
[[ -n $common_handler ]] || common_handler="trap ERR"
common.GetOptions "$@"
shift "$((OPTIND + 1))"
[[ -z $common_command ]] || common_command+="=$"
common_command+='("$common_function" "$@")'
set -E
set +e
trap "common.ErrHandler" ERR
try
eval "$common_command"
yrt
catch; do
"$common_unhandled" >&2
hctac
[[ $common_flags == *E* ]] || set +E
[[ $common_flags != *e* ]] || set -e
[[ $common_flags != *f* || $- == *f* ]] || set -f
[[ $common_flags == *f* || $- != *f* ]] || set +f
eval "$common_handler"
}
下面是一个示例，它假设上面的脚本存储在名为simple的文件中。makefifo文件包含这个答案中描述的脚本。假设名为4444kkkkk的文件不存在，因此会发生异常。ls 4444kkkkk命令的错误消息输出将被自动抑制，直到进入适当的捕获块。
#!/bin/bash
#
if [[ $0 != ${BASH_SOURCE[0]} ]]; then
bash "${BASH_SOURCE[0]}" "$@"
return
fi
source simple
source makefifo
MyFunction3() {
echo "entered MyFunction3" >&4
echo "This is from MyFunction3"
ls 4444kkkkk
echo "leaving MyFunction3" >&4
}
MyFunction2() {
echo "entered MyFunction2" >&4
value="$(MyFunction3)"
echo "leaving MyFunction2" >&4
}
MyFunction1() {
echo "entered MyFunction1" >&4
local "flag=false"
try
(
echo "start of try" >&4
MyFunction2
echo "end of try" >&4
)
yrt
catch "[1-3]" "*" "Exception\ Type:\ ERR"; do
echo 'start of catch "[1-3]" "*" "Exception\ Type:\ ERR"'
local -i "i"
echo "-------------------------------------------------"
echo "Status: $(GetStatus)"
echo "Messages:"
for ((i=0; i<$(MessageCount); i++)); do
echo "$(GetMessage "$i")"
done
echo "-------------------------------------------------"
break
echo 'end of catch "[1-3]" "*" "Exception\ Type:\ ERR"'
hctac >&4
catch "1 3 5" "*" -n "Exception\ Type:\ ERR"; do
echo 'start of catch "1 3 5" "*" -n "Exception\ Type:\ ERR"'
echo "-------------------------------------------------"
echo "Status: $(GetStatus)"
[[ $(MessageCount) -le 1 ]] || echo "$(GetMessage "1")"
echo "-------------------------------------------------"
break
echo 'end of catch "1 3 5" "*" -n "Exception\ Type:\ ERR"'
hctac >&4
catch; do
echo 'start of catch' >&4
echo "failure"
flag="true"
echo 'end of catch' >&4
hctac
finally
echo "in finally"
yllanif >&4
"$flag" || echo "success"
echo "leaving MyFunction1" >&4
} 2>&6
ErrHandler() {
echo "EOF"
DefaultErrHandler "$@"
echo "Function: $3"
while read; do
[[ $REPLY != *EOF ]] || break
echo "$REPLY"
done
}
set -u
echo "starting" >&2
MakeFIFO "6"
TryCatchFinally -e -h ErrHandler -o /dev/fd/4 -v result /dev/fd/6 MyFunction1 4>&2
echo "result=$result"
exec >&6-
上面的脚本使用GNU bash, version 3.2.57(1)-release (x86_64-apple-darwin17)进行了测试。运行此脚本的输出如下所示。
starting
entered MyFunction1
start of try
entered MyFunction2
entered MyFunction3
start of catch "[1-3]" "*" "Exception\ Type:\ ERR"
-------------------------------------------------
Status: 1
Messages:
Orginal Status: 1
Exception Type: ERR
Function: MyFunction3
ls: 4444kkkkk: No such file or directory
-------------------------------------------------
start of catch
end of catch
in finally
leaving MyFunction1
result=failure
另一个使用throw的例子可以通过用下面的脚本替换函数MyFunction3来创建。
MyFunction3() {
echo "entered MyFunction3" >&4
echo "This is from MyFunction3"
throw "3" "Orginal Status: 3" "Exception Type: throw"
echo "leaving MyFunction3" >&4
}
throw命令的语法如下所示。如果没有参数，则使用存储在变量中的状态和消息。
throw [status] [message ...]
执行修改后的脚本的输出如下所示。
starting
entered MyFunction1
start of try
entered MyFunction2
entered MyFunction3
start of catch "1 3 5" "*" -n "Exception\ Type:\ ERR"
-------------------------------------------------
Status: 3
Exception Type: throw
-------------------------------------------------
start of catch
end of catch
in finally
leaving MyFunction1
result=failure
其他回答
根据我在这里找到的一些答案，我为自己的项目制作了一个小的帮助文件:
trycatch.sh
#!/bin/bash
function try()
{
[[ $- = *e* ]]; SAVED_OPT_E=$?
set +e
}
function throw()
{
exit $1
}
function catch()
{
export ex_code=$?
(( $SAVED_OPT_E )) && set +e
return $ex_code
}
function throwErrors()
{
set -e
}
function ignoreErrors()
{
set +e
}
下面是它在使用中的示例:
#!/bin/bash
export AnException=100
export AnotherException=101
# start with a try
try
( # open a subshell !!!
echo "do something"
[ someErrorCondition ] && throw $AnException
echo "do something more"
executeCommandThatMightFail || throw $AnotherException
throwErrors # automaticatly end the try block, if command-result is non-null
echo "now on to something completely different"
executeCommandThatMightFail
echo "it's a wonder we came so far"
executeCommandThatFailsForSure || true # ignore a single failing command
ignoreErrors # ignore failures of commands until further notice
executeCommand1ThatFailsForSure
local result = $(executeCommand2ThatFailsForSure)
[ result != "expected error" ] && throw $AnException # ok, if it's not an expected error, we want to bail out!
executeCommand3ThatFailsForSure
# make sure to clear $ex_code, otherwise catch * will run
# echo "finished" does the trick for this example
echo "finished"
)
# directly after closing the subshell you need to connect a group to the catch using ||
catch || {
# now you can handle
case $ex_code in
$AnException)
echo "AnException was thrown"
;;
$AnotherException)
echo "AnotherException was thrown"
;;
*)
echo "An unexpected exception was thrown"
throw $ex_code # you can rethrow the "exception" causing the script to exit if not caught
;;
esac
}
Bash不会在检测到错误状态时中止正在运行的执行(除非您设置了-e标志)。提供try/catch的编程语言这样做是为了抑制由于这种特殊情况而产生的“保释”(因此通常称为“异常”)。
相反，在bash中，只有有问题的命令将退出，退出码大于0，表示错误状态。当然，您可以检查这一点，但由于没有任何自动保释，因此try/catch没有意义。它只是缺乏背景。
然而，你可以通过使用子壳来模拟一个保释，它可以在你决定的点终止:
(
echo "Do one thing"
echo "Do another thing"
if some_condition
then
exit 3 # <-- this is our simulated bailing out
fi
echo "Do yet another thing"
echo "And do a last thing"
) # <-- here we arrive after the simulated bailing out, and $? will be 3 (exit code)
if [ $? = 3 ]
then
echo "Bail out detected"
fi
而不是some_condition的if你也可以尝试一个命令，如果它失败(退出码大于0)，保释:
(
echo "Do one thing"
echo "Do another thing"
some_command || exit 3
echo "Do yet another thing"
echo "And do a last thing"
)
...
不幸的是，使用这种技术只能使用255个不同的退出码(1..255)，而且不能使用像样的异常对象。
如果你需要更多的信息来传递模拟异常，你可以使用subshell的stdout，但这有点复杂，可能是另一个问题;-)
使用上面提到的-e标志，你甚至可以剥离显式的退出语句:
(
set -e
echo "Do one thing"
echo "Do another thing"
some_command
echo "Do yet another thing"
echo "And do a last thing"
)
...
假设终端应用名为'app'(你希望它在你的$PATH中):
if [[ ! `which app` ]]; then
# run code if app not installed
else
# run code if app is installed
fi
有很多类似的解决方案可能会起作用。下面是一个简单有效的方法来完成try/catch，并在评论中进行了解释。
#!/bin/bash
function a() {
# do some stuff here
}
function b() {
# do more stuff here
}
# this subshell is a scope of try
# try
(
# this flag will make to exit from current subshell on any error
# inside it (all functions run inside will also break on any error)
set -e
a
b
# do more stuff here
)
# and here we catch errors
# catch
errorCode=$?
if [ $errorCode -ne 0 ]; then
echo "We have an error"
# We exit the all script with the same error, if you don't want to
# exit it and continue, just delete this line.
exit $errorCode
fi
正如大家所说，bash没有适当的语言支持的try/catch语法。您可以使用-e参数启动bash，或者在脚本中使用set -e来中止整个bash进程，如果任何命令有非零退出码的话。(你也可以设置+e来临时允许失败的命令。)
因此，模拟try/catch块的一种技术是在启用-e的情况下启动子进程来完成工作。然后在主进程中，检查子进程的返回码。
Bash支持heredoc字符串，因此不需要编写两个单独的文件来处理这个问题。在下面的示例中，TRY heredoc将在单独的bash实例中运行，并启用了-e，因此如果任何命令返回非零退出码，子进程将崩溃。然后，回到主进程，我们可以检查返回代码以处理一个catch块。
#!/bin/bash
set +e
bash -e <<TRY
echo hello
cd /does/not/exist
echo world
TRY
if [ $? -ne 0 ]; then
echo caught exception
fi
它不是一个适当的语言支持的try/catch块，但它可能会为您带来类似的体验。
