{"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\/hu\/blog\/administrirovanie\/sem-neozhidannyh-peremennyh-bash","title":{"rendered":"H\u00e9t meglep\u0151 Bash v\u00e1ltoz\u00f3","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Folytatva a kev\u00e9sb\u00e9 ismert funkci\u00f3kr\u00f3l<\/a><\/noindex> a bash-ban, bemutatok h\u00e9t v\u00e1ltoz\u00f3t, amelyr\u0151l tal\u00e1n nem is tudt\u00e1l.<\/a><\/noindex> PROMPT_COMMAND<\/p>\n

1) Lehet, hogy m\u00e1r tiszt\u00e1ban vagy azzal, hogyan manipul\u00e1lhatod a prompt \u00fczenetet, hogy k\u00fcl\u00f6nb\u00f6z\u0151 hasznos inform\u00e1ci\u00f3kat mutasson, de nem mindenki tudja, hogy a prompt minden megjelen\u00edt\u00e9sekor shell parancs futtathat\u00f3.<\/code><\/h4>\n

\nVal\u00f3j\u00e1ban sok bonyolult prompt manipul\u00e1tor haszn\u00e1lja ezt a v\u00e1ltoz\u00f3t inform\u00e1ci\u00f3k gy\u0171jt\u00e9s\u00e9re, amely megjelenik a promptban.<\/p>\n

Pr\u00f3b\u00e1ld ki ezt egy \u00faj shellben, \u00e9s n\u00e9zd meg, mi t\u00f6rt\u00e9nik a munkamenettel:<\/p>\n

$ PROMPT_COMMAND='echo -n \"writing the prompt at \" && date'<\/p>\n

HISTTIMEFORMAT<\/code><\/pre>\n
<\/a><\/noindex><\/p>\n
2) A konzolban megkapod a kor\u00e1bban a fi\u00f3koddal v\u00e9grehajtott parancsok list\u00e1j\u00e1t.<\/code><\/h4>\n
\nHa futtatjuk a history<\/code> $ HISTTIMEFORMAT='I ran this at: %d\/%m\/%y %T '<\/p>\n
Miut\u00e1n be\u00e1ll\u00edtottad ezt a v\u00e1ltoz\u00f3t, az \u00faj bejegyz\u00e9sek id\u0151t is r\u00f6gz\u00edtenek a parancs mellett, \u00edgy a kimenet \u00edgy fog kin\u00e9zni:<\/code><\/pre>\n
\n1871  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 -<\/p>\n
A form\u00e1tum megfelel a<\/pre>\n
\nman date CDPATH<\/code>.<\/p>\n
3) Az id\u0151 megtakar\u00edt\u00e1s\u00e1hoz a parancssorban ezt a v\u00e1ltoz\u00f3t haszn\u00e1lhatod a k\u00f6nyvt\u00e1rak olyan k\u00f6nny\u0171 megv\u00e1ltoztat\u00e1s\u00e1ra, mint ahogyan a parancsokat h\u00edvod.<\/code><\/h4>\n
\nMint a<\/p>\n
, a v\u00e1ltoz\u00f3 PATH<\/code>egy kett\u0151sponttal elv\u00e1lasztott \u00fatvonalak list\u00e1j\u00e1t tartalmazza. Amikor a parancsot relat\u00edv \u00faton ind\u00edtod el (azaz perjel n\u00e9lk\u00fcl az elej\u00e9n), a shell alap\u00e9rtelmez\u00e9s szerint a helyi mapp\u00e1dban keres megfelel\u0151 neveket. Az id\u0151 megtakar\u00edt\u00e1s\u00e1hoz a parancssorban ezt a v\u00e1ltoz\u00f3t haszn\u00e1lhatod a k\u00f6nyvt\u00e1rak olyan k\u00f6nny\u0171 megv\u00e1ltoztat\u00e1s\u00e1ra, mint ahogyan a parancsokat h\u00edvod.<\/code> keresni fog az \u00fcres k\u00f6nyvt\u00e1rakban, ahov\u00e1 \u00e1t szeretn\u00e9l l\u00e9pni. cd<\/code> Ha \u00fagy \u00e1ll\u00edtod be: Az id\u0151 megtakar\u00edt\u00e1s\u00e1hoz a parancssorban ezt a v\u00e1ltoz\u00f3t haszn\u00e1lhatod a k\u00f6nyvt\u00e1rak olyan k\u00f6nny\u0171 megv\u00e1ltoztat\u00e1s\u00e1ra, mint ahogyan a parancsokat h\u00edvod.<\/code> $ CDPATH=\/:\/lib<\/p>\n
majd be\u00edrod: Az id\u0151 megtakar\u00edt\u00e1s\u00e1hoz a parancssorban ezt a v\u00e1ltoz\u00f3t haszn\u00e1lhatod a k\u00f6nyvt\u00e1rak olyan k\u00f6nny\u0171 megv\u00e1ltoztat\u00e1s\u00e1ra, mint ahogyan a parancsokat h\u00edvod.<\/code> $ cd \/home\n$ cd tmp<\/p>\n
akkor mindig el fogsz jutni a<\/code><\/pre>\n
\nf\u00fcggetlen\u00fcl att\u00f3l, hol vagy.<\/p>\n
De \u00f3vatosan, mert ha a list\u00e1ban nem szerepel a helyi (<\/code><\/pre>\n
\n) mappa, nem tudsz l\u00e9trehozni m\u00e1s mapp\u00e1t \/tmp<\/code> tmp<\/p>\n
\u00e9s nem tudsz \u00e1tmenni hozz\u00e1, ahogy \u00e1ltal\u00e1ban szokt\u00e1l:.<\/code>$ cd \/home\n$ mkdir tmp\n$ cd tmp\n$ pwd\n\/tmp Ups!<\/code> Ez olyan z\u0171rzavarnak t\u0171nik, amit \u00e9reztem, amikor r\u00e1j\u00f6ttem, hogy a helyi mappa nem volt benne a ismertebb v\u00e1ltoz\u00f3ban<\/p>\n
\u2026 de ezt a PATH v\u00e1ltoz\u00f3ban kell elk\u00e9sz\u00edtenem, mert megt\u00e9veszthetnek, ha futtatnak egy hamis parancsot egy let\u00f6lt\u00f6tt k\u00f3db\u00f3l.<\/code><\/pre>\n
\nAz \u00e9n be\u00e1ll\u00edt\u00e1som kezd\u0151pont:<\/p>\n
CDPATH=.:\/space:\/etc:\/var\/lib:\/usr\/share:\/opt PATH<\/code>SHLVL<\/p>\n
Valaha is gondolt\u00e1l arra, hogy be\u00edrsz<\/p>\n
CDPATH=.:\/space:\/etc:\/var\/lib:\/usr\/share:\/opt<\/code><\/pre>\n
<\/p>\n
4) SHLVL<\/code><\/h4>\n
\nValaha gondolt\u00e1l arra, hogy be\u00edrsz exit<\/code> kib\u00fajik a jelenlegi bash shellb\u0151l egy m\u00e1sik \"sz\u00fcl\u0151\" shellbe, vagy egyszer\u0171en csak teljesen bez\u00e1rja a konzolablakot?<\/p>\n
Ez a v\u00e1ltoz\u00f3 k\u00f6veti, hogy milyen m\u00e9lyen vagyunk a bash shellben. Ha \u00faj termin\u00e1lt nyitunk, akkor 1-re van \u00e1ll\u00edtva:<\/p>\n
$ echo $SHLVL\n1<\/code><\/pre>\n
\nAzt\u00e1n, ha elind\u00edtunk egy m\u00e1sik shell folyamatot, a sz\u00e1m n\u0151:<\/p>\n
$ bash\n$ echo $SHLVL\n2<\/code><\/pre>\n
\nEz nagyon hasznos lehet szkriptekben, ahol nem biztos, hogy ki kell-e l\u00e9pni, vagy nyomon kell k\u00f6vetni, hogy hol tartunk a be\u00e1gyaz\u00e1sban.<\/p>\n
5) LINENO<\/code><\/h4>\n
\nA pillanatnyi \u00e1llapot elemz\u00e9s\u00e9hez \u00e9s hibakeres\u00e9shez a v\u00e1ltoz\u00f3 is hasznos LINENO<\/code>, amely megadja a jelenlegi munkamenetben v\u00e9grehajtott parancsok sz\u00e1m\u00e1t:<\/p>\n
$ bash\n$ echo $LINENO\n1\n$ echo $LINENO\n2<\/code><\/pre>\n
\nEz leggyakrabban szkriptek hibakeres\u00e9s\u00e9n\u00e9l haszn\u00e1latos. Olyan sorokat besz\u00farva, mint echo DEBUG:$LINENO<\/code>, gyorsan meghat\u00e1rozhatja, hogy hol tart a szkripten bel\u00fcl (vagy sem).<\/p>\n
6) REPLY<\/code><\/h4>\n
\nHa, mint \u00e9n, \u00e1ltal\u00e1ban ilyen k\u00f3dot \u00edrsz:<\/p>\n
$ read input\necho csin\u00e1lj valamit $input<\/code><\/pre>\n
\nakkor meglepet\u00e9s lehet, hogy nem sz\u00fcks\u00e9ges v\u00e1ltoz\u00f3t l\u00e9trehozni:<\/p>\n
$ read\necho csin\u00e1lj valamit a $REPLY-vel<\/code><\/pre>\n
\nEz ugyanazt csin\u00e1lja.<\/p>\n
7) TMOUT<\/code><\/h4>\n
\nAnnak \u00e9rdek\u00e9ben, hogy ne maradjunk t\u00fal sok\u00e1ig a termel\u00e9si szervereken biztons\u00e1gi okokb\u00f3l, vagy v\u00e9letlen\u00fcl ne ind\u00edtsunk el valami vesz\u00e9lyeset a helytelen termin\u00e1lban, e v\u00e1ltoz\u00f3 be\u00e1ll\u00edt\u00e1sa v\u00e9delmi funkci\u00f3t l\u00e1t el.<\/p>\n
Ha semmit nem \u00edrunk be a be\u00e1ll\u00edtott m\u00e1sodpercek alatt, a shellb\u0151l val\u00f3 kil\u00e9p\u00e9s t\u00f6rt\u00e9nik.<\/p>\n
Teh\u00e1t ez alternat\u00edv\u00e1ja sleep 1 && exit<\/code>:<\/p>\n
$ TMOUT=1<\/code><\/pre>\n
Forr\u00e1s: habr.com<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"
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