bash 如何在bash脚本中获取文件的第一行？
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How to get the first line of a file in a bash script?
提问by Neuquino
I have to put in a bash variable the first line of a file. I guess it is with the grep command, but it is any way to restrict the number of lines?
我必须在文件的第一行放入一个 bash 变量。我猜是用 grep 命令，但是有什么办法可以限制行数吗？
回答by sth
headtakes the first lines from a file, and the -nparameter can be used to specify how many lines should be extracted:
head从文件中获取第一行，该-n参数可用于指定应提取多少行：
line=$(head -n 1 filename)
回答by ghostdog74
to read first line using bash, use readstatement. eg
要使用 bash 读取第一行，请使用read语句。例如
read -r firstline<file
firstlinewill be your variable (No need to assign to another)
firstline将是您的变量（无需分配给另一个）
回答by fedorqui 'SO stop harming'
This suffices and stores the first line of filenamein the variable $line:
这足以将第一行存储filename在变量中$line：
read -r line < filename
I also like awkfor this:
我也喜欢awk这个：
awk 'NR==1 {print; exit}' file
To store the line itself, use the var=$(command)syntax. In this case, line=$(awk 'NR==1 {print; exit}' file).
要存储行本身，请使用var=$(command)语法。在这种情况下，line=$(awk 'NR==1 {print; exit}' file)。
Or even sed:
甚至sed：
sed -n '1p' file
With the equivalent line=$(sed -n '1p' file).
与line=$(sed -n '1p' file).
See a sample when we feed the readwith seq 10, that is, a sequence of numbers from 1 to 10:
当我们输入readwith时看一个示例seq 10，即从 1 到 10 的数字序列：
$ read -r line < <(seq 10)
$ echo "$line"
1
$ line=$(awk 'NR==1 {print; exit}' <(seq 10))
$ echo "$line"
1
回答by Hymanbot
line=$(head -1 file)
Will work fine. (As previous answer). But
会工作得很好。（如上一个答案）。但
line=$(read -r FIRSTLINE < filename)
will be marginally faster as readis a built-in bash command.
read与内置 bash 命令一样，速度会稍快一些。
回答by openwonk
Just echothe first list of your source file into your target file.
只需echo将您的源文件的第一个列表放入您的目标文件中。
echo $(head -n 1 source.txt) > target.txt
回答by Neil McGill
The question didn't ask which is fastest, but to add to the sed answer, -n '1p' is badly performing as the pattern space is still scanned on large files. Out of curiosity I found that 'head' wins over sed narrowly:
问题没有问哪个最快，但要添加到 sed 答案中， -n '1p' 表现不佳，因为仍然在大文件上扫描模式空间。出于好奇，我发现 'head' 以微弱优势胜过 sed：
# best:
head -n1 $bigfile >/dev/null
# a bit slower than head (I saw about 10% difference):
sed '1q' $bigfile >/dev/null
# VERY slow:
sed -n '1p' $bigfile >/dev/null
