如何从后台进程linux shell脚本获取结果?
例如,假设我要计算10个大文件的行数,并打印总数如何从后台进程linux shell脚本获取结果?,linux,shell,command-line,Linux,Shell,Command Line,例如,假设我要计算10个大文件的行数,并打印总数 for f in files do #this creates a background process for each file wc -l $f | awk '{print $1}' & done 我试着说: for f in files do #this does not work :/ n=$( expr $(wc -l $f | awk '{print $1}') + $n ) & d
for f in files
do
#this creates a background process for each file
wc -l $f | awk '{print $1}' &
done
我试着说:
for f in files
do
#this does not work :/
n=$( expr $(wc -l $f | awk '{print $1}') + $n ) &
done
echo $n
我终于找到了一个使用匿名管道和bash的有效解决方案:
#!/bin/bash
# this executes a separate shell and opens a new pipe, where the
# reading endpoint is fd 3 in our shell and the writing endpoint
# stdout of the other process. Note that you don't need the
# background operator (&) as exec starts a completely independent process.
exec 3< <(./a.sh 2&1)
# ... do other stuff
# write the contents of the pipe to a variable. If the other process
# hasn't already terminated, cat will block.
output=$(cat <&3)
#/bin/bash
#这将执行一个单独的shell并打开一个新管道,其中
#在我们的shell中,读取端点是fd3,写入端点是fd3
#另一个进程的stdout。请注意,您不需要
#后台操作员(&)作为exec启动一个完全独立的进程。
exec 3<您可以将其写入文件或更好的方式,在数据到达时立即收听fifo
下面是一个关于它们如何工作的小例子:
# create the fifo
mkfifo test
# listen to it
while true; do if read line <test; then echo $line; fi done
# in another shell
echo 'hi there'
# notice 'hi there' being printed in the first shell
并在fifo上收听大小。您可能应该使用gnu并行:
find . -maxdepth 1 -type f | parallel --gnu 'wc -l' | awk 'BEGIN {n=0} {n += $1} END {print n}'
或者并行模式下的xargs:
find . -maxdepth 1 -type f | xargs -n1 -P4 wc -l | awk 'BEGIN {n=0} {n += $1} END {print n}'
如果这不符合您的需要,另一个选择是写入临时文件。如果不想写入磁盘,只需写入/dev/shm即可。这是大多数Linux系统上的ramdisk
#!/bin/bash
declare -a temp_files
count=0
for f in *
do
if [[ -f "$f" ]]; then
temp_files[$count]="$(mktemp /dev/shm/${f}-XXXXXX)"
((count++))
fi
done
count=0
for f in *
do
if [[ -f "$f" ]]; then
cat "$f" | wc -l > "${temp_files[$count]}" &
((count++))
fi
done
wait
cat "${temp_files[@]}" | awk 'BEGIN {n=0} {n += $1} END {print n}'
for tf in "${temp_files[@]}"
do
rm "$tf"
done
顺便说一下,这可以看作是一个map reduce,wc进行映射,awk进行缩减。我认为这将创建一个名为“3”的文件。我正在尝试不写入disk.find-maxdepth 1-type f | xargs-n1-P4 wc-l | awk'BEGIN{n=0}{n+=1}END{print n}工作得非常完美。但我选择了/dev/shm,因为我喜欢有一个动态的后台进程数。您可能需要小心一点,如果您有1000个文件,最终将有1000个进程,这可能会使您的机器陷入困境。这需要一些额外的工作来确保进程数量的限制。我会,现在我有10个文件,大小大约为20-30GB。
#!/bin/bash
declare -a temp_files
count=0
for f in *
do
if [[ -f "$f" ]]; then
temp_files[$count]="$(mktemp /dev/shm/${f}-XXXXXX)"
((count++))
fi
done
count=0
for f in *
do
if [[ -f "$f" ]]; then
cat "$f" | wc -l > "${temp_files[$count]}" &
((count++))
fi
done
wait
cat "${temp_files[@]}" | awk 'BEGIN {n=0} {n += $1} END {print n}'
for tf in "${temp_files[@]}"
do
rm "$tf"
done