{"id":33494,"date":"2019-10-31T21:52:52","date_gmt":"2019-10-31T18:52:52","guid":{"rendered":"https:\/\/prohoster.info\/blog\/sem-neozhidannyh-peremennyh-bash\/"},"modified":"2019-10-31T21:52:52","modified_gmt":"2019-10-31T18:52:52","slug":"sem-neozhidannyh-peremennyh-bash","status":"publish","type":"post","link":"https:\/\/prohoster.info\/sv\/blog\/administrirovanie\/sem-neozhidannyh-peremennyh-bash","title":{"rendered":"Sju ov\u00e4ntade Bash-variabler","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Forts\u00e4tta serien av anteckningar om mindre k\u00e4nda<\/a><\/noindex> funktioner<\/a><\/noindex> i bash, kommer jag att visa dig sju variabler som du kanske inte k\u00e4nner till.<\/p>\n

1) PROMPT_COMMAND<\/code><\/h4>\n

\nKanske \u00e4r du redan medveten om hur man manipulerar prompten f\u00f6r att visa olika nyttig information, men inte alla vet att varje g\u00e5ng prompten visas kan man k\u00f6ra ett skalkommando.<\/p>\n

Faktum \u00e4r att m\u00e5nga avancerade promptmanipulatorer anv\u00e4nder denna variabel f\u00f6r att k\u00f6ra kommandon f\u00f6r att samla information som visas i prompten.<\/p>\n

F\u00f6rs\u00f6k att k\u00f6ra detta i en ny shell och se vad som h\u00e4nder med sessionen:<\/p>\n

$ PROMPT_COMMAND='echo -n \"writing the prompt at \" && date'<\/code><\/pre>\n
<\/a><\/noindex><\/p>\n
2) HISTTIMEFORMAT<\/code><\/h4>\n
\nOm du k\u00f6r history<\/code> i konsolen f\u00e5r du en lista \u00f6ver kommandon som tidigare k\u00f6rts under ditt konto.<\/p>\n
$ HISTTIMEFORMAT='I ran this at: %d\/%m\/%y %T '<\/code><\/pre>\n
\nN\u00e4r denna variabel har st\u00e4llts in, registreras nya poster med tid tillsammans med kommandot, s\u00e5 utfallet kommer att se ut s\u00e5 h\u00e4r:<\/p>\n
1871  I ran this at: 01\/05\/19 13:38:07 cat \/etc\/resolv.conf\n1872  I ran this at: 01\/05\/19 13:38:19 curl bbc.co.uk\n1873  I ran this at: 01\/05\/19 13:38:41 sudo vi \/etc\/resolv.conf\n1874  I ran this at: 01\/05\/19 13:39:18 curl -vvv bbc.co.uk\n1876  I ran this at: 01\/05\/19 13:39:25 sudo su -<\/pre>\n
\nFormateringen \u00f6verensst\u00e4mmer med tecknen fr\u00e5n man date<\/code>.<\/p>\n
3) CDPATH<\/code><\/h4>\n
\nF\u00f6r att spara tid i kommandoraden kan du anv\u00e4nda denna variabel f\u00f6r att \u00e4ndra kataloger lika enkelt som du k\u00f6r kommandon.<\/p>\n
Precis som PATH<\/code>, variabeln CDPATH<\/code> \u00e4r en lista med s\u00f6kv\u00e4gar som \u00e4r \u00e5tskilda med kolon. N\u00e4r du k\u00f6r ett kommando cd<\/code> med en relativ s\u00f6kv\u00e4g (d.v.s. utan snedstreck i b\u00f6rjan), letar skalet som standard i din aktuella mapp efter motsvarande namn. CDPATH<\/code> kommer att s\u00f6ka i de v\u00e4gar som du angav f\u00f6r katalogen du vill g\u00e5 till.<\/p>\n
Om du st\u00e4ller in CDPATH<\/code> s\u00e5 h\u00e4r:<\/p>\n
$ CDPATH=\/:\/lib<\/code><\/pre>\n
\noch sedan skriver:<\/p>\n
$ cd \/home\n$ cd tmp<\/code><\/pre>\n
\n\u00e5ker du alltid till \/tmp<\/code> oavsett var du befinner dig.<\/p>\n
Men var f\u00f6rsiktig, f\u00f6r om du inte inkluderar den lokala (.<\/code>) mappen i listan, kan du inte skapa n\u00e5gon annan mapp tmp<\/code> och g\u00e5 till den som vanligt:<\/p>\n
$ cd \/home\n$ mkdir tmp\n$ cd tmp\n$ pwd\n\/tmp<\/code><\/pre>\n
\nOops!<\/p>\n
Detta verkar vara f\u00f6rvirring, vilket jag k\u00e4nde n\u00e4r jag ins\u00e5g att den lokala mappen inte var inkluderad i den mer bekanta variabeln PATH<\/code>\u2026 men du m\u00e5ste g\u00f6ra detta i PATH-variabeln, f\u00f6r du kan bli lurad genom att k\u00f6ra ett falskt kommando fr\u00e5n n\u00e5gon nedladdad kod.<\/p>\n
Min s\u00e4tts som startpunkt:<\/p>\n
CDPATH=.:\/space:\/etc:\/var\/lib:\/usr\/share:\/opt<\/code><\/pre>\n
<\/p>\n
4) SHLVL<\/code><\/h4>\n
\nHar du n\u00e5gonsin undrat, skriver exit<\/code> kommer att ta dig ur den aktuella bash-skalen till en annan \"f\u00f6r\u00e4lderskal\" eller helt enkelt st\u00e4nga konsolf\u00f6nstret?<\/p>\n
Denna variabel sp\u00e5rar hur djupt du \u00e4r inb\u00e4ddad i bash-skalet. Om du \u00f6ppnar en ny terminal s\u00e4tts den till 1:<\/p>\n
$ echo $SHLVL\n1<\/code><\/pre>\n
\nSedan, om du k\u00f6r en annan skalprocess, \u00f6kar siffran:<\/p>\n
$ bash\n$ echo $SHLVL\n2<\/code><\/pre>\n
\nDetta kan vara mycket anv\u00e4ndbart i skript d\u00e4r du inte \u00e4r s\u00e4ker p\u00e5 om du ska st\u00e4nga eller inte, eller f\u00f6r att sp\u00e5ra var du befinner dig i inb\u00e4ddningen.<\/p>\n
5) LINENO<\/code><\/h4>\n
\n\u00c4ven f\u00f6r att analysera det aktuella tillst\u00e5ndet och f\u00f6r fels\u00f6kning \u00e4r variabeln LINENO<\/code>, som rapporterar antalet kommandon som k\u00f6rts i sessionen fram till nu:<\/p>\n
$ bash\n$ echo $LINENO\n1\n$ echo $LINENO\n2<\/code><\/pre>\n
\nDetta anv\u00e4nds oftast vid fels\u00f6kning av skript. Genom att infoga s\u00e5dana rader som echo DEBUG:$LINENO<\/code>, kan du snabbt avg\u00f6ra var du befinner dig i skriptet (eller inte).<\/p>\n
6) REPLY<\/code><\/h4>\n
\nOm du, precis som jag, oftast skriver s\u00e5dan kod:<\/p>\n
$ read input\necho g\u00f6r n\u00e5got med $input<\/code><\/pre>\n
\nkan det bli en \u00f6verraskning att du inte beh\u00f6ver oroa dig f\u00f6r att skapa en variabel \u00f6verhuvudtaget:<\/p>\n
$ read\necho g\u00f6r n\u00e5got med $REPLY<\/code><\/pre>\n
\nDet g\u00f6r samma sak.<\/p>\n
7) TMOUT<\/code><\/h4>\n
\nF\u00f6r att inte stanna f\u00f6r l\u00e4nge p\u00e5 produktionsservrar av s\u00e4kerhetssk\u00e4l eller av misstag k\u00f6ra n\u00e5got farligt i fel terminal, s\u00e5 fungerar inst\u00e4llning av denna variabel som ett skydd.<\/p>\n
Om inget matas in under det angivna antalet sekunder, sker en utloggning fr\u00e5n skalet.<\/p>\n
Detta \u00e4r, allts\u00e5, ett alternativ till sleep 1 && exit<\/code>:<\/p>\n
$ TMOUT=1<\/code><\/pre>\n
K\u00e4lla: habr.com<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"
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