使用head命令和tail命令显示指定的行：
head
-n, --lines=[-]K
print the first K lines instead of the first 10; with the leading
‘-’, print all but the last K lines of each file
tail
-n, --lines=K
output the last K lines, instead of the last 10; or use -n +K to
output lines starting with the Kth
[root@localhost etc]# pwd
/etc
[root@localhost etc]# cat yum.conf
[main]
cachedir=/var/cache/yum/$basearch/$releasever
keepcache=0
debuglevel=2
logfile=/var/log/yum.log
exactarch=1
obsoletes=1
gpgcheck=1
plugins=1
installonly_limit=3
//此处是一空行
# This is the default, if you make this bigger yum won't see if the metadata
# is newer on the remote and so you'll "gain" the bandwidth of not having to
# download the new metadata and "pay" for it by yum not having correct
# information.
# It is esp. important, to have correct metadata, for distributions like
# Fedora which don't keep old packages around. If you don't like this checking
# interupting your command line usage, it's much better to have something
# manually check the metadata once an hour (yum-updatesd will do this).
# metadata_expire=90m
//此处是一空行
# PUT YOUR REPOS HERE OR IN separate files named file.repo
# in /etc/yum.repos.d
[root@localhost etc]# cat yum.conf |wc -l
23
yum.conf文件共有23行
[root@localhost etc]# head yum.conf
[main]
cachedir=/var/cache/yum/$basearch/$releasever
keepcache=0
debuglevel=2
logfile=/var/log/yum.log
exactarch=1
obsoletes=1
gpgcheck=1
plugins=1
installonly_limit=3
显示前10行，这个是默认值
[root@localhost etc]# head -n 2 yum.conf
[main]
cachedir=/var/cache/yum/$basearch/$releasever
显示前2行
[root@localhost etc]# head -n -20 yum.conf
[main]
cachedir=/var/cache/yum/$basearch/$releasever
keepcache=0
显示除最后20行以外的所有行
[root@localhost etc]# tail yum.conf
# download the new metadata and "pay" for it by yum not having correct
# information.
# It is esp. important, to have correct metadata, for distributions like
# Fedora which don't keep old packages around. If you don't like this checking
# interupting your command line usage, it's much better to have something
# manually check the metadata once an hour (yum-updatesd will do this).
# metadata_expire=90m
//此处是一空行
# PUT YOUR REPOS HERE OR IN separate files named file.repo
# in /etc/yum.repos.d
显示最后10行，这是默认值
[root@localhost etc]# tail -n 2 yum.conf
# PUT YOUR REPOS HERE OR IN separate files named file.repo
# in /etc/yum.repos.d
显示最后2行
[root@localhost etc]# tail -n +21 yum.conf
//此处是一空行
# PUT YOUR REPOS HERE OR IN separate files named file.repo
# in /etc/yum.repos.d
从第21行开始显示后面的所有行，即第21行到第23行
显示第11行到第20行(总共23行)：
从第11行开始显示，但不包括最后3行
[huage@localhost etc]$ head -n -3 yum.conf |tail -n +11
显示前20行，但从第11行开始
[huage@localhost etc]$ head -n 20 yum.conf |tail -n +11
显示除最后3行以外的所有行，但只显示最后10行
[huage@localhost etc]$ head -n -3 yum.conf |tail -n 10
显示前20行中的后10行
[huage@localhost etc]$ head -n 20 yum.conf |tail -n 10
从第11行开始显示，但只显示前10行
[huage@localhost etc]$ tail -n +11 yum.conf |head -n 10
从第11行开始显示，但不包括最后3行
[huage@localhost etc]$ tail -n +11 yum.conf |head -n -3
显示最后13行中的前10行
[huage@localhost etc]$ tail -n 13 yum.conf |head -n 10
显示最后13行中除末尾的3行以外的前10行
[huage@localhost etc]$ tail -n 13 yum.conf |head -n -3
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