在 bash 中一次一行读取多个文件

在 bash 中一次一行读取多个文件

我知道在 bash 中读取命令的基本方法:

cal | while IFS= read -r line ; do 
    echo X${line}X
done

但是,如果我想循环读取多个文件/命令中的一行怎么办?我尝试过命名管道,但它们只吐出一行。

$ cal > myfifo &
$ IFS= read -r line < myfifo
[cal exits]
$ echo $line
   February 2015      

所以我真正想要的是这样的:

while [all pipes are not done]; do
    IFS=
    read line1 < pipe1    # reading one line from this one
    read line2 < pipe2    # and one line from this one
    read line3 < pipe3    # and one line from this one
    print things with $line1 $line2 and $line3
done

总体而言,我想做的是处理来自 cal 的三个不同月份的数据,进行一些着色以供 Conky 使用。老实说,这有点像刮牦牛毛,所以在这一点上已经成为学术和“学习经历”。

答案1

paste将是最简洁的方法。但是,使用 bash 文件描述符和进程替换:

exec 3< <(cal 1 2015)
exec 4< <(cal 2 2015)
exec 5< <(cal 3 2015)

while IFS= read -r -u3 line1; do
    IFS= read -r -u4 line2
    IFS= read -r -u5 line3
    printf "%-25s%-25s%-25s\n" "$line1" "$line2" "$line3"
done

exec 3<&-
exec 4<&-
exec 5<&-
    January 2015             February 2015             March 2015          
Su Mo Tu We Th Fr Sa     Su Mo Tu We Th Fr Sa     Su Mo Tu We Th Fr Sa     
             1  2  3      1  2  3  4  5  6  7      1  2  3  4  5  6  7     
 4  5  6  7  8  9 10      8  9 10 11 12 13 14      8  9 10 11 12 13 14     
11 12 13 14 15 16 17     15 16 17 18 19 20 21     15 16 17 18 19 20 21     
18 19 20 21 22 23 24     22 23 24 25 26 27 28     22 23 24 25 26 27 28     
25 26 27 28 29 30 31                              29 30 31                 

答案2

您可以使用paste组合输出,然后按行读取:

paste -d $'\n' <(foo) <(bar) <(cat baz) | while IFS= read -r line1
do
    IFS= read -r line2 || break
    IFS= read -r line3 || break
    # ..
done

答案3

这就是您需要的结构。

您的 FIFO 位于正确的行上,但当您从中读取一行时退出的原因calread -r line < myfifo打开了 FIFO,读取了一行,然后再次关闭了它。关闭管道会向另一端发送一个信号,表明无法再进行写入(读取)操作。于是cal退出了。

# Create the FIFOs
mknod pipe1 p
mknod pipe2 p
mknod pipe3 p

# Start off the commands
command1 >pipe1 &
command2 >pipe2 &
command3 >pipe3 &

# Attach file descriptors to the other side of the FIFOs
exec 11<pipe1 12<pipe2 13<pipe3

# Loop
IS_MORE=0
while [[ 0 eq $IS_MORE ]]
do
    IS_MORE=1
    read LINE1 <&11 && IS_MORE=0
    read LINE2 <&12 && IS_MORE=0
    read LINE3 <&13 && IS_MORE=0
    # ...
done

# Close descriptors and remove the FIFOs
exec 11<&- 12<&- 13<&-
rm -f pipe1 pipe2 pipe3

# Clean up the dead processes (zombies)
wait

# ...

答案4

while \
    IFS= read -r -u3 line1;do
    IFS= read -r -u4 line2
    IFS= read -r -u5 line3
    printf "%-25s%-25s%-25s\n" "$line1" "$line2" "$line3"
done 3< <(cal -h 1 2018) 4< <(cal -h 2 2018) 5< <(cal -h 3 2018)

或者如果 3 个月是相邻的,则可能是以下内容:

while IFS= read -r;do
    printf "%s\n" "${REPLY}"
done < <(cal -A 1 -B 1 -h 8 2018)

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