7.环境变量 cp mv cat more less head tail

2.10 环境变量PATH

# echo $PATH

/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin

# echo "PATH=$PATH:/tmp" >> /etc/profile

Environment stuff goes in /etc/profile

System wide environment and startup programs, for login setup

# vi .bash_profile

# Get the aliases and functions

if [ -f ~/.bashrc ]; then

. ~/.bashrc

fi

# User specific environment and startup programs

PATH=$PATH:$HOME/bin

export PATH

2.11 cp命令

cp

Copy SOURCE to DEST, or multiple SOURCE(s) to DIRECTORY.

-l, --link

hard link files instead of copying

# cp -l test test_hd

-R, -r, --recursive

copy directories recursively

# cp -r 1.d/ 2.d/

-s, --symbolic-link

make symbolic links instead of copying

# cp -s test test_so

-v, --verbose

explain what is being done

# cp 2.d 5.d -rv

"2.d" -> "5.d"

"2.d/1.d" -> "5.d/1.d"

2.12 mv命令

mv - Rename SOURCE to DEST, or move SOURCE(s) to DIRECTORY.

-i, --interactive

prompt before overwrite

# mv -i 1 2

mv：是否覆盖"2"？

2.13 文档查看cat_more_less_head_tail

cat - Concatenate FILE(s), or standard input, to standard output.

-E, --show-ends

display $ at end of each line

# cat -E /etc/passwd

root:x:0:0:root:/root:/bin/bash$

bin:x:1:1:bin:/bin:/sbin/nologin$

daemon:x:2:2:daemon:/sbin:/sbin/nologin$

-n, --number

number all output lines

# cat -n /etc/passwd

1 root:x:0:0:root:/root:/bin/bash

2 bin:x:1:1:bin:/bin:/sbin/nologin

3 daemon:x:2:2:daemon:/sbin:/sbin/nologin

tac - Write each FILE to standard output, last line first.

With no FILE, or when FILE is -, read standard input.

# tac /etc/passwd

chrony:x:998:996::/var/lib/chrony:/sbin/nologin

sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin

postfix:x:89:89::/var/spool/postfix:/sbin/nologin

more is a filter for paging through text one screenful at a time.Users should realize that less(1) provides more(1) emulation plus extensive enhancements.

SPACE Display next k lines of text. Defaults to current screen size.

RETURN Display next k lines of text. Defaults to 1. Argument becomes new default.

f Skip forward k screenfuls of text. Defaults to 1.

b or ^B Skip backwards k screenfuls of text. Defaults to 1.

´ Go to place where previous search started.

/pattern Search for kth occurrence of regular expression. Defaults to 1.

n Search for kth occurrence of last regular expression. Defaults to 1.

:f Display current file name and line number.

less - opposite of more

SPACE or ^V or f or ^F

Scroll forward N lines, default one window (see option -z below).

ENTER or RETURN or ^N or e or ^E or j or ^J

Scroll forward N lines, default 1.

b or ^B or ESC-v

Scroll backward N lines, default one window (see option -z below).

F Scroll forward, and keep trying to read when the end of file is reached.

g or < or ESC-<

Go to line N in the file, default 1 (beginning of file).

G or > or ESC->

Go to line N in the file, default the end of the file.

/pattern

Search forward in the file for the N-th line containing the pattern.

?pattern

Search backward in the file for the N-th line containing the pattern.

n Repeat previous search, for N-th line containing the last pattern.

N Repeat previous search, but in the reverse direction.

head Print the first 10 lines of each FILE to standard output.

-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

# head -2 anaconda-ks.cfg

#version=DEVEL

# System authorization information

# wc -l anaconda-ks.cfg

51 anaconda-ks.cfg

# head -n -50 anaconda-ks.cfg

#version=DEVEL

-q, --quiet, --silent

never print headers giving file names

-v, --verbose

always print headers giving file names

# head -v anaconda-ks.cfg

==> anaconda-ks.cfg <==

#version=DEVEL

# System authorization information

auth --enableshadow --passalgo=sha512

tail Print the last 10 lines of each FILE to standard output.

-f, --follow[={name|descriptor}]

output appended data as the file grows;

-n, --lines=K

output the last K lines, instead of the last 10;

or use -n +K to output starting with the Kth

# tail -2 anaconda-ks.cfg

pwpolicy luks --minlen=6 --minquality=1 --notstrict --nochanges --notempty

%end

# wc -l anaconda-ks.cfg

51 anaconda-ks.cfg

# tail -n +51 anaconda-ks.cfg

%end

tailf、tail -f、tail -F三者区别

tail -f      等同于--follow=descriptor，根据文件描述符进行追踪，当文件改名或被删除，追踪停止

tail -F     等同于--follow=name  --retry，根据文件名进行追踪，并保持重试，即该文件被删除或改名后，如果再次创建相同的文件名，会继续追踪

tailf        等同于tail -f -n 10（貌似tail -f或-F默认也是打印最后10行，然后追踪文件），与tail -f不同的是，如果文件不增长，它不会去访问磁盘文件，所以tailf特别适合那些便携机上跟踪日志文件，因为它减少了磁盘访问，可以省电

tailf命令几乎等同于tail -f，严格说来应该与tail --follow=name更相似些。当文件改名之后它也能继续跟踪，特别适合于日志文件的跟踪（follow the growth of a log file）。与tail -f不同的是，如果文件不增长，它不会去访问磁盘文件（It is similar to tail -f but does not access the file when it is not growing.  This has the side effect of not updating the access  time for the file, so a filesystem flush does not occur periodically when no log activity is happening.）。tailf特别适合那些便携机上跟踪日志文件，因为它能省电，因为减少了磁盘访问嘛（tailf  is extremely useful for monitoring log files on a laptop when logging is infrequent and the user desires that the hard disk spin down to conserve battery life.）