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1：環(huán)境變量

在bash shell中環(huán)境變量分為兩類(lèi)：

全局環(huán)境變量
局部環(huán)境變量

1.1：全局環(huán)境變量：

全局環(huán)境變量不僅對(duì)shell可見(jiàn)，對(duì)所有shell創(chuàng)建的子進(jìn)程（也可認(rèn)作為子shell）可見(jiàn)。這對(duì)那些子進(jìn)程中獲取父進(jìn)程信息的程序很是有用。系統(tǒng)在開(kāi)始bash會(huì)話之前就設(shè)置了一些全局的環(huán)境變量?？赏ㄟ^(guò)evn(printevn)命令查看：

zhangshuisheng:~ zhangshuisheng$ env
TERM_PROGRAM=Apple_Terminal
TERM=xterm-256color
SHELL=/bin/bash
TMPDIR=/var/folders/5n/ss3mb0bd6yj2vdn6tzdsgkdm0000gn/T/
Apple_PubSub_Socket_Render=/private/tmp/com.apple.launchd.x65L1DoqVs/Render
TERM_PROGRAM_VERSION=361.1
TERM_SESSION_ID=88C746B4-CC31-4B2A-9055-0E7378B20FF1
USER=zhangshuisheng
SSH_AUTH_SOCK=/private/tmp/com.apple.launchd.OehhRVr1Ma/Listeners
__CF_USER_TEXT_ENCODING=0x1F5:0x19:0x34
PATH=/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin
PWD=/Users/zhangshuisheng
LANG=zh_CN.UTF-8
ITERM_PROFILE=Default
XPC_FLAGS=0x0
XPC_SERVICE_NAME=0
COLORFGBG=7;0
SHLVL=2
HOME=/Users/zhangshuisheng
ITERM_SESSION_ID=w0t0p1:B3299AC3-4FFA-4304-A846-F504A06FED39
LOGNAME=zhangshuisheng
SECURITYSESSIONID=186a8
_=/usr/bin/env
OLDPWD=/Users/zhangshuisheng/work/shell
zhangshuisheng:~ zhangshuisheng$

可以明顯看出，這些預(yù)設(shè)的全局環(huán)境變量大部分都是用戶(hù)登入系統(tǒng)時(shí)設(shè)置的。顯示其中的單個(gè)環(huán)境變量可使用echo輸出，如：

zhangshuisheng:~ zhangshuisheng$ echo $HOME
/Users/zhangshuisheng

1.2：局部環(huán)境變量

局部變量只可在定義它的進(jìn)程（或認(rèn)為成shell）中可見(jiàn)，沒(méi)有什么操作命令可以單獨(dú)查看系統(tǒng)預(yù)設(shè)的局部環(huán)境變量，但是可以使用set命令查看所有的系統(tǒng)變量（包括全局和局部環(huán)境變量）如：

zhangshuisheng:~ zhangshuisheng$ set
Apple_PubSub_Socket_Render=/private/tmp/com.apple.launchd.x65L1DoqVs/Render
BASH=/bin/bash
BASH_ARGC=()
BASH_ARGV=()
BASH_LINENO=()
BASH_REMATCH=([0]="g")
BASH_SOURCE=()
BASH_VERSINFO=([0]="3" [1]="2" [2]="57" [3]="1" [4]="release" [5]="x86_64-apple-darwin15")
BASH_VERSION='3.2.57(1)-release'
COLORFGBG='7;0'
COLUMNS=80
DIRSTACK=()
EUID=501
GROUPS=()
HISTFILE=/Users/zhangshuisheng/.bash_sessions/88C746B4-CC31-4B2A-9055-0E7378B20FF1.historynew
HISTFILESIZE=500
HISTSIZE=500
HOME=/Users/zhangshuisheng
HOSTNAME=zhangshuisheng.lan
HOSTTYPE=x86_64
IFS=$' \t\n'
ITERM_PROFILE=Default
ITERM_SESSION_ID=w0t0p1:B3299AC3-4FFA-4304-A846-F504A06FED39
LANG=zh_CN.UTF-8
LINES=24
LOGNAME=zhangshuisheng
MACHTYPE=x86_64-apple-darwin15
MAILCHECK=60
OLDPWD=/Users/zhangshuisheng/work/shell
OPTERR=1
OPTIND=1
OSTYPE=darwin15
PATH=/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin
PIPESTATUS=([0]="0")
PPID=9164
PROMPT_COMMAND=update_terminal_cwd
PS1='\h:\W \u\$ '
PS2='> '
PS4='+ '
PWD=/Users/zhangshuisheng
SECURITYSESSIONID=186a8
SHELL=/bin/bash
SHELLOPTS=braceexpand:emacs:hashall:histexpand:history:interactive-comments:monitor
SHELL_SESSION_DID_HISTORY_CHECK=1
SHELL_SESSION_DID_INIT=1
SHELL_SESSION_DIR=/Users/zhangshuisheng/.bash_sessions
SHELL_SESSION_FILE=/Users/zhangshuisheng/.bash_sessions/88C746B4-CC31-4B2A-9055-0E7378B20FF1.session
SHELL_SESSION_HISTFILE=/Users/zhangshuisheng/.bash_sessions/88C746B4-CC31-4B2A-9055-0E7378B20FF1.history
SHELL_SESSION_HISTFILE_NEW=/Users/zhangshuisheng/.bash_sessions/88C746B4-CC31-4B2A-9055-0E7378B20FF1.historynew
SHELL_SESSION_HISTFILE_SHARED=/Users/zhangshuisheng/.bash_history
SHELL_SESSION_HISTORY=1
SHELL_SESSION_TIMESTAMP_FILE=/Users/zhangshuisheng/.bash_sessions/_expiration_check_timestamp
SHLVL=2
SSH_AUTH_SOCK=/private/tmp/com.apple.launchd.OehhRVr1Ma/Listeners
TERM=xterm-256color
TERM_PROGRAM=Apple_Terminal
TERM_PROGRAM_VERSION=361.1
TERM_SESSION_ID=88C746B4-CC31-4B2A-9055-0E7378B20FF1
TMPDIR=/var/folders/5n/ss3mb0bd6yj2vdn6tzdsgkdm0000gn/T/
UID=501
USER=zhangshuisheng
XPC_FLAGS=0x0
XPC_SERVICE_NAME=0
_=clear
__CF_USER_TEXT_ENCODING=0x1F5:0x19:0x34
shell_session_delete_expired () 
{ 
    if ( [ ! -e "$SHELL_SESSION_TIMESTAMP_FILE" ] || [ -z $(find "$SHELL_SESSION_TIMESTAMP_FILE" -mtime -1d) ] ); then
        local expiration_lock_file="$SHELL_SESSION_DIR/_expiration_lockfile";
        if shlock -f "$expiration_lock_file" -p $$; then
            echo -n 'Deleting expired sessions...';
            local delete_count=$(find "$SHELL_SESSION_DIR" -type f -mtime +2w -print -delete | wc -l);
            [ "$delete_count" -gt 0 ] && echo $delete_count' completed.' || echo 'none found.';
            touch "$SHELL_SESSION_TIMESTAMP_FILE";
            rm "$expiration_lock_file";
        fi;
    fi
}
shell_session_history_allowed () 
{ 
    if [ -n "$HISTFILE" ]; then
        local allowed=0;
        if shopt -q histappend || [ -n "$HISTTIMEFORMAT" ]; then
            allowed=${SHELL_SESSION_HISTORY:-0};
        else
            allowed=${SHELL_SESSION_HISTORY:=1};
        fi;
        if [ $allowed -eq 1 ]; then
            return 0;
        fi;
    fi;
    return 1
}
shell_session_history_check () 
{ 
    if [ ${SHELL_SESSION_DID_HISTORY_CHECK:-0} -eq 0 ]; then
        SHELL_SESSION_DID_HISTORY_CHECK=1;
        if shell_session_history_allowed; then
            shell_session_history_enable;
        fi;
        if [ "$PROMPT_COMMAND" = "shell_session_history_check" ]; then
            unset PROMPT_COMMAND;
        else
            if [[ $PROMPT_COMMAND =~ (.*)(; *shell_session_history_check *| *shell_session_history_check *; *)(.*) ]]; then
                PROMPT_COMMAND="${BASH_REMATCH[1]}${BASH_REMATCH[3]}";
            fi;
        fi;
    fi
}
shell_session_history_enable () 
{ 
    touch "$SHELL_SESSION_HISTFILE_NEW";
    HISTFILE="$SHELL_SESSION_HISTFILE_NEW";
    SHELL_SESSION_HISTORY=1
}
shell_session_save () 
{ 
    if [ -n "$SHELL_SESSION_FILE" ]; then
        echo -n 'Saving session...';
        echo echo Restored session: $(date) >|"$SHELL_SESSION_FILE";
        declare -F shell_session_save_user_state > /dev/null && shell_session_save_user_state;
        shell_session_history_allowed && shell_session_save_history;
        echo 'completed.';
    fi
}
shell_session_save_history () 
{ 
    shell_session_history_enable;
    history -a;
    if [ -f "$SHELL_SESSION_HISTFILE_SHARED" ] && [ ! -s "$SHELL_SESSION_HISTFILE" ]; then
        echo -ne '\n...copying shared history...';
        cp "$SHELL_SESSION_HISTFILE_SHARED" "$SHELL_SESSION_HISTFILE";
    fi;
    echo -ne '\n...saving history...';
    cat "$SHELL_SESSION_HISTFILE_NEW" >> "$SHELL_SESSION_HISTFILE_SHARED";
    cat "$SHELL_SESSION_HISTFILE_NEW" >> "$SHELL_SESSION_HISTFILE";
    : >|"$SHELL_SESSION_HISTFILE_NEW";
    if [ -n "$HISTFILESIZE" ]; then
        echo -n 'truncating history files...';
        HISTFILE="$SHELL_SESSION_HISTFILE_SHARED";
        HISTFILESIZE="$HISTFILESIZE";
        HISTFILE="$SHELL_SESSION_HISTFILE";
        HISTFILESIZE="$size";
        HISTFILE="$SHELL_SESSION_HISTFILE_NEW";
    fi;
    echo -ne '\n...'
}
shell_session_update () 
{ 
    shell_session_save && shell_session_delete_expired
}
update_terminal_cwd () 
{ 
    local url_path='';
    { 
        local i ch hexch LC_CTYPE=C LC_ALL=;
        for ((i = 0; i < ${#PWD}; ++i))
        do
            ch="${PWD:i:1}";
            if [[ "$ch" =~ [/._~A-Za-z0-9-] ]]; then
                url_path+="$ch";
            else
                printf -v hexch "%02X" "'$ch";
                url_path+="%${hexch: -2:2}";
            fi;
        done
    };
    printf '\e]7;%s\a' "file://$HOSTNAME$url_path"
}

從輸出可以看出，不僅包含了操作env命令時(shí)輸出的全局的系統(tǒng)變量，還有輸出其他的局部變量。

2：設(shè)置環(huán)境變量

2.1：設(shè)置局部變量

zhangshuisheng:~ zhangshuisheng$ test="hello shell"
zhangshuisheng:~ zhangshuisheng$ echo $test 
hello shell
zhangshuisheng:~ zhangshuisheng$ bash
bash-3.2$ echo $test

bash-3.2$

注：示例展示了局部環(huán)境變量的設(shè)置（test="hello shell"）和可見(jiàn)性(局部環(huán)境變量盡在創(chuàng)建他的shell中可用)

2.2：設(shè)置全局環(huán)境變量(export)

zhangshuisheng:~ zhangshuisheng$ export text1="a beautiful day"
zhangshuisheng:~ zhangshuisheng$ echo $text1 
a beautiful day
zhangshuisheng:~ zhangshuisheng$ bash
bash-3.2$ echo $text1
a beautiful day
bash-3.2$ exit
exit
zhangshuisheng:~ zhangshuisheng$ export test
zhangshuisheng:~ zhangshuisheng$ echo $test 
hello shell
zhangshuisheng:~ zhangshuisheng$ bash
bash-3.2$ echo $test
hello shell
bash-3.2$

注：全局環(huán)境變量可以通過(guò)export來(lái)設(shè)置。通過(guò)上面示例可看出：可以使用export直接來(lái)設(shè)置一個(gè)全局環(huán)境變量，也可以使用它把局部環(huán)境變量導(dǎo)出為全局環(huán)境變量。全局環(huán)境變量在所有子進(jìn)程（shell）中都可見(jiàn)

2.3：刪除環(huán)境變量(unset)

zhangshuisheng:~ zhangshuisheng$ unset test
zhangshuisheng:~ zhangshuisheng$ echo $test 

zhangshuisheng:~ zhangshuisheng$ unset $text1 
zhangshuisheng:~ zhangshuisheng$ echo $text1
a beautiful day
zhangshuisheng:~ zhangshuisheng$ unset text1 
zhangshuisheng:~ zhangshuisheng$ echo $text1

zhangshuisheng:~ zhangshuisheng$

注：通過(guò)上面實(shí)例可以看出，unset在刪除環(huán)境變量時(shí)直接加載變量名前面空格隔開(kāi)，變量名前不能加$

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系統(tǒng)變量

系統(tǒng)變量

1：環(huán)境變量

1.1：全局環(huán)境變量：

1.2：局部環(huán)境變量

2：設(shè)置環(huán)境變量

2.1：設(shè)置局部變量

2.2：設(shè)置全局環(huán)境變量(export)

2.3：刪除環(huán)境變量(unset)

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系統(tǒng)變量

1：環(huán)境變量

1.1：全局環(huán)境變量：

1.2：局部環(huán)境變量

2：設(shè)置環(huán)境變量

2.1：設(shè)置局部變量

2.2：設(shè)置全局環(huán)境變量(export)

2.3：刪除環(huán)境變量(unset)

相關(guān)閱讀更多精彩內(nèi)容

友情鏈接更多精彩內(nèi)容

色偷偷精品伊人,欧洲久久精品,欧美综合婷婷骚逼,国产AV主播,国产最新探花在线,九色在线视频一区,伊人大交九欧美,1769亚洲,黄色成人av