正确计算bash变量的行数

时间:2014-05-19 11:27:07

标签: bash shell wc

我需要计算给定变量的行数。例如,我需要找到VAR有多少行,VAR=$(git log -n 10 --format="%s")

我尝试了echo "$VAR" | wc -l),这确实有效,但如果VAR为空,则打印1,这是错误的。这有解决方法吗?比使用if子句检查变量是否为空更好...(可能添加一行并从返回的值中减去1)。

4 个答案:

答案 0 :(得分:13)

wc计算换行符数。您可以使用grep -c '^'来计算行数。 您可以看到与以下区别:

#!/bin/bash

count_it() {
    echo "Variablie contains $2: ==>$1<=="
    echo -n 'grep:'; echo -n "$1" | grep -c '^'
    echo -n 'wc  :'; echo -n "$1" | 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"

产生什么:

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

答案 1 :(得分:6)

你总是可以有条件地写下来:

[ -n "$VAR" ] && echo "$VAR" | wc -l || echo 0

这将检查$VAR是否包含内容并采取相应行动。

答案 2 :(得分:5)

对于纯粹的bash解决方案:不是将git命令的输出放入变量(可以说是丑陋的),而是将它放在一个数组中,每个字段一行:

mapfile -t ary < <(git log -n 10 --format="%s")

然后您只需要计算数组ary中的字段数:

echo "${#ary[@]}"

如果您需要检索第5条提交消息,此设计也会让您的生活变得更简单:

echo "${ary[4]}"

答案 3 :(得分:2)

尝试:

echo "$VAR" | grep ^ | wc -l