正确计算 bash 变量的行数
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Correctly count number of lines a bash variable
提问by linkyndy
I need to count the number of lines of a given variable. For example I need to find how many lines VARhas, where VAR=$(git log -n 10 --format="%s").
我需要计算给定变量的行数。例如，我需要找到有多少行VAR，在哪里VAR=$(git log -n 10 --format="%s")。
I tried with echo "$VAR" | wc -l), which indeed works, but if VARis empty, is prints 1, which is wrong. Is there a workaround for this? Something better than using an ifclause to check whether the variable is empty...(maybe add a line and subtract 1 from the returned value?).
我试过echo "$VAR" | wc -l)，确实有效，但如果VAR为空，则为 prints 1，这是错误的。有解决方法吗？比使用if子句检查变量是否为空更好的东西......（也许添加一行并从返回值中减去 1？）。
回答by jm666
The wccounts the number of newline chars. You can use grep -c '^'for counting lines.
You can see the difference with:
该wc计数换行字符的数量。您可以grep -c '^'用于计数线。你可以看到不同之处：
#!/bin/bash
count_it() {
echo "Variablie contains : ==><=="
echo -n 'grep:'; echo -n "" | grep -c '^'
echo -n 'wc :'; echo -n "" | wc -l
echo
}
VAR=''
count_it "$VAR" "empty variable"
VAR='one line'
count_it "$VAR" "one line without \n at the end"
VAR='line1
'
count_it "$VAR" "one line with \n at the end"
VAR='line1
line2'
count_it "$VAR" "two lines without \n at the end"
VAR='line1
line2
'
count_it "$VAR" "two lines with \n at the end"
what produces:
什么产生：
Variablie contains empty variable: ==><==
grep:0
wc : 0
Variablie contains one line without \n at the end: ==>one line<==
grep:1
wc : 0
Variablie contains one line with \n at the end: ==>line1
<==
grep:1
wc : 1
Variablie contains two lines without \n at the end: ==>line1
line2<==
grep:2
wc : 1
Variablie contains two lines with \n at the end: ==>line1
line2
<==
grep:2
wc : 2
回答by nemo
You can always write it conditionally:
你总是可以有条件地写：
[ -n "$VAR" ] && echo "$VAR" | wc -l || echo 0
This will check whether $VARhas contents and act accordingly.
这将检查是否$VAR有内容并采取相应措施。
回答by gniourf_gniourf
For a pure bash solution: instead of putting the output of the gitcommand into a variable (which, arguably, is ugly), put it in an array, one line per field:
对于纯 bash 解决方案：不是将git命令的输出放入变量（这可以说是丑陋的），而是将其放入一个数组中，每个字段一行：
mapfile -t ary < <(git log -n 10 --format="%s")
Then you only need to count the number of fields in the array ary:
然后你只需要计算数组中的字段数ary：
echo "${#ary[@]}"
This design will also make your life simpler if, e.g., you need to retrieve the 5th commit message:
如果例如您需要检索第 5 个提交消息，则此设计还将使您的生活更简单：
echo "${ary[4]}"
回答by Taher Khorshidi
try:
尝试：
echo "$VAR" | grep ^ | wc -l
