{"id":174,"date":"2009-01-15T19:54:48","date_gmt":"2009-01-15T17:54:48","guid":{"rendered":"http:\/\/michauko.org\/blog\/?p=174"},"modified":"2009-10-08T15:06:04","modified_gmt":"2009-10-08T13:06:04","slug":"ifs-separateurs-scripts-bash","status":"publish","type":"post","link":"https:\/\/michauko.org\/blog\/ifs-separateurs-scripts-bash-174\/","title":{"rendered":"IFS : s\u00e9parateurs & scripts BASH"},"content":{"rendered":"

Un truc qui m’a pris la t\u00eate il f\u00fbt un temps et plus r\u00e9cemment, pour une question de syntaxe oubli\u00e9e.
\nVoil\u00e0 le topo : vous faites un rapide script BASH<\/a> pour faire tel ou tel traitement sur des fichiers. Et l\u00e0, chaque espace dans un nom de fichier vous met en l’air votre script car c’est vu comme \u00ab\u00a0un saut de ligne\u00a0\u00bb, dirons-nous.
\nIl faut alors penser \u00e0 jouer avec le \u00ab\u00a0Internal Field Separator\u00a0\u00bb – IFS – pour indiquer \u00e0 BASH<\/a> quel(s) caract\u00e8re(s) consid\u00e9rer comme saut de ligne.
\nPar d\u00e9faut, on trouve le saut de ligne \u00ab\u00a0\\n\u00a0\u00bb, mais aussi la tabulation (\u00ab\u00a0\\t\u00a0\u00bb) et l’espace !!!<\/strong><\/p>\n

Simplification possible du probl\u00e8me : un extr\u00eamiste pinguiste vous dira simplement que les espaces dans un nom de fichier, c’est mal. Ca a beau \u00eatre mal, qui n’a jamais coll\u00e9 un espace dans un nom de fichier ? qui a le choix de ne pas le faire ? ou de tuer ses gentils utilisateurs le faisant ?<\/em><\/p>\n

En images, \u00e7a donne \u00e7a :<\/p>\n

user@srv:\/tmp$ echo >> liste\r\nchamp1.1;champ1.2;champ1.3\r\nchamp2.1;champ avec espace;champ2.3\r\nchamp   avec_tabulation;champ3.2;champ pour finir\r\nCTRL-D pour finir la saisie\r\n\r\nuser@srv:\/tmp$ for i in `cat liste`\r\n> do\r\n> echo $i\r\n> done\r\nchamp1.1;champ1.2;champ1.3\r\nchamp2.1;champ\r\navec\r\nespace;champ2.3\r\nchamp\r\navec_tabulation;champ3.2;champ\r\npour\r\nfinir<\/pre>\n
Houuu le vilain r\u00e9sultat pour quelqu’un qui voulait voir afficher 3 lignes, pour par exemple faire un \u00ab\u00a0awk -F ‘;’ ‘{print $1 ou $2 ou $3}’ pour r\u00e9cup\u00e9rer tel ou tel champ d’un fichier CSV.
\nNotez que le \u00ab\u00a0$i\u00a0\u00bb ne changera rien par rapport au $i.<\/p>\n
Solution : red\u00e9finir l’IFS.
\nD’abord le on le sauvegarde car c’est pas simple de taper son contenu, la preuve, affichez cette variable, elle semble vide :<\/p>\n
user@srv:\/tmp$ echo $IFS\r\n\r\nuser@srv:\/tmp$\r\n<\/pre>\n
La difficult\u00e9 de syntaxe mentionn\u00e9e au d\u00e9but de l’article est de faire gober le \u00ab\u00a0\\n\u00a0\u00bb sans interpr\u00e9tation par le shell, voici comment faire dans le cas qui nous int\u00e9resse : (le reste est expliqu\u00e9 sur wikipedia<\/a>)<\/p>\n
user@srv: \/tmp$ OLDIFS=$IFS\r\nuser@srv:\/tmp$ IFS=$'\\n'\r\nuser@srv:\/tmp$ for i in `cat liste`; do echo \"$i\"; done\r\nchamp1.1;champ1.2;champ1.3\r\nchamp2.1;champ avec espace;champ2.3\r\nchamp   avec_tabulation;champ3.2;champ pour finir\r\n<\/pre>\n
A noter que votre variable IFS restera en l’\u00e9tat pendant toute votre session (ie, votre shell ouvert). Donc n’oubliez pas de r\u00e9tablir IFS=$OLDIFS.
\nSi vous faites ceci dans un script, c’est alors propre \u00e0 l’ex\u00e9cution du script.<\/p>\n
Enfin, pour les bidouilleux, \u00e7a peut permettra de faire du d\u00e9coupage assez bizzarement :<\/p>\n
user@srv:\/tmp$ IFS=a\r\nuser@srv:\/tmp$ for i in `cat liste`; do echo \"$i\"; done\r\nch\r\nmp1.1;ch\r\nmp1.2;ch\r\nmp1.3\r\nch\r\nmp2.1;ch\r\nmp\r\nvec esp\r\nce;ch\r\nmp2.3\r\nch\r\nmp\r\nvec_t\r\nbul\r\ntion;ch\r\nmp3.2;ch\r\nmp pour finir\r\n<\/pre>\n","protected":false},"excerpt":{"rendered":"
Un truc qui m’a pris la t\u00eate il f\u00fbt un temps et plus r\u00e9cemment, pour une question de syntaxe oubli\u00e9e. Voil\u00e0 le topo : vous faites un rapide script BASH pour faire tel ou tel …<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_crdt_document":"","_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[2,387,82,83],"tags":[276,275,274,273],"class_list":["post-174","post","type-post","status-publish","format-standard","hentry","category-debian","category-ligne-de-commande","category-pl","category-ubuntu","tag-awk","tag-bash","tag-csv","tag-ifs"],"yoast_head":"\nIFS : s\u00e9parateurs & scripts BASH - Le blog de Michauko<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/michauko.org\/blog\/ifs-separateurs-scripts-bash-174\/\" \/>\n<meta property=\"og:locale\" content=\"fr_FR\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"IFS : s\u00e9parateurs & scripts BASH - Le blog de Michauko\" \/>\n<meta property=\"og:description\" content=\"Un truc qui m’a pris la t\u00eate il f\u00fbt un temps et plus r\u00e9cemment, pour une question de syntaxe oubli\u00e9e. 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